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e8b9727835
sqlite/src/where.c
drh e8b9727835 More refactoring in where.c. (CVS 2552) 
FossilOrigin-Name: a35bd50af8961133adc66e40c38402e81a02bb56
2005-07-19 22:22:12 +00:00

1564 lines
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C
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/*
** 2001 September 15
**
** The author disclaims copyright to this source code. In place of
** a legal notice, here is a blessing:
**
** May you do good and not evil.
** May you find forgiveness for yourself and forgive others.
** May you share freely, never taking more than you give.
**
*************************************************************************
** This module contains C code that generates VDBE code used to process
** the WHERE clause of SQL statements. This module is reponsible for
** generating the code that loops through a table looking for applicable
** rows. Indices are selected and used to speed the search when doing
** so is applicable. Because this module is responsible for selecting
** indices, you might also think of this module as the "query optimizer".
**
** $Id: where.c,v 1.147 2005/07/19 22:22:13 drh Exp $
*/
#include "sqliteInt.h"
/*
** The number of bits in a Bitmask. "BMS" means "BitMask Size".
*/
#define BMS (sizeof(Bitmask)*8-1)
/*
** Determine the number of elements in an array.
*/
#define ARRAYSIZE(X) (sizeof(X)/sizeof(X[0]))
/* Forward reference
*/
typedef struct WhereClause WhereClause;
/*
** The query generator uses an array of instances of this structure to
** help it analyze the subexpressions of the WHERE clause. Each WHERE
** clause subexpression is separated from the others by an AND operator.
**
** All WhereTerms are collected into a single WhereClause structure.
** The following identity holds:
**
** WhereTerm.pWC->a[WhereTerm.idx] == WhereTerm
**
** When a term is of the form:
**
** X <op> <expr>
**
** where X is a column name and <op> is one of certain operators,
** then WhereTerm.leftCursor and WhereTerm.leftColumn record the
** cursor number and column number for X.
**
** prereqRight and prereqAll record sets of cursor numbers,
** but they do so indirectly. A single ExprMaskSet structure translates
** cursor number into bits and the translated bit is stored in the prereq
** fields. The translation is used in order to maximize the number of
** bits that will fit in a Bitmask. The VDBE cursor numbers might be
** spread out over the non-negative integers. For example, the cursor
** numbers might be 3, 8, 9, 10, 20, 23, 41, and 45. The ExprMaskSet
** translates these sparse cursor numbers into consecutive integers
** beginning with 0 in order to make the best possible use of the available
** bits in the Bitmask. So, in the example above, the cursor numbers
** would be mapped into integers 0 through 7.
*/
typedef struct WhereTerm WhereTerm;
struct WhereTerm {
Expr *pExpr; /* Pointer to the subexpression */
u16 idx; /* Index of this term in pWC->a[] */
i16 iPartner; /* Disable pWC->a[iPartner] when this term disabled */
u16 flags; /* Bit flags. See below */
i16 leftCursor; /* Cursor number of X in "X <op> <expr>" */
i16 leftColumn; /* Column number of X in "X <op> <expr>" */
WhereClause *pWC; /* The clause this term is part of */
Bitmask prereqRight; /* Bitmask of tables used by pRight */
Bitmask prereqAll; /* Bitmask of tables referenced by p */
};
/*
** Allowed values of WhereTerm.flags
*/
#define TERM_DYNAMIC 0x0001 /* Need to call sqlite3ExprDelete(p) */
#define TERM_VIRTUAL 0x0002 /* Added by the optimizer. Do not code */
#define TERM_CODED 0x0004 /* This term is already coded */
/*
** An instance of the following structure holds all information about a
** WHERE clause. Mostly this is a container for one or more WhereTerms.
*/
struct WhereClause {
int nTerm; /* Number of terms */
int nSlot; /* Number of entries in a[] */
WhereTerm *a; /* Pointer to an array of terms */
WhereTerm aStatic[10]; /* Initial static space for the terms */
};
/*
** An instance of the following structure keeps track of a mapping
** between VDBE cursor numbers and bits of the bitmasks in WhereTerm.
**
** The VDBE cursor numbers are small integers contained in
** SrcList_item.iCursor and Expr.iTable fields. For any given WHERE
** clause, the cursor numbers might not begin with 0 and they might
** contain gaps in the numbering sequence. But we want to make maximum
** use of the bits in our bitmasks. This structure provides a mapping
** from the sparse cursor numbers into consecutive integers beginning
** with 0.
**
** If ExprMaskSet.ix[A]==B it means that The A-th bit of a Bitmask
** corresponds VDBE cursor number B. The A-th bit of a bitmask is 1<<A.
**
** For example, if the WHERE clause expression used these VDBE
** cursors: 4, 5, 8, 29, 57, 73. Then the ExprMaskSet structure
** would map those cursor numbers into bits 0 through 5.
**
** Note that the mapping is not necessarily ordered. In the example
** above, the mapping might go like this: 4->3, 5->1, 8->2, 29->0,
** 57->5, 73->4. Or one of 719 other combinations might be used. It
** does not really matter. What is important is that sparse cursor
** numbers all get mapped into bit numbers that begin with 0 and contain
** no gaps.
*/
typedef struct ExprMaskSet ExprMaskSet;
struct ExprMaskSet {
int n; /* Number of assigned cursor values */
int ix[sizeof(Bitmask)*8]; /* Cursor assigned to each bit */
};
/*
** Initialize a preallocated WhereClause structure.
*/
static void whereClauseInit(WhereClause *pWC){
pWC->nTerm = 0;
pWC->nSlot = ARRAYSIZE(pWC->aStatic);
pWC->a = pWC->aStatic;
}
/*
** Deallocate a WhereClause structure. The WhereClause structure
** itself is not freed. This routine is the inverse of whereClauseInit().
*/
static void whereClauseClear(WhereClause *pWC){
int i;
WhereTerm *a;
for(i=pWC->nTerm-1, a=pWC->a; i>=0; i--, a++){
if( a->flags & TERM_DYNAMIC ){
sqlite3ExprDelete(a->pExpr);
}
}
if( pWC->a!=pWC->aStatic ){
sqliteFree(pWC->a);
}
}
/*
** Add a new entries to the WhereClause structure. Increase the allocated
** space as necessary.
*/
static WhereTerm *whereClauseInsert(WhereClause *pWC, Expr *p, int flags){
WhereTerm *pTerm;
if( pWC->nTerm>=pWC->nSlot ){
WhereTerm *pOld = pWC->a;
pWC->a = sqliteMalloc( sizeof(pWC->a[0])*pWC->nSlot*2 );
if( pWC->a==0 ) return 0;
memcpy(pWC->a, pOld, sizeof(pWC->a[0])*pWC->nTerm);
if( pOld!=pWC->aStatic ){
sqliteFree(pOld);
}
pWC->nSlot *= 2;
}
pTerm = &pWC->a[pWC->nTerm];
pTerm->idx = pWC->nTerm;
pWC->nTerm++;
pTerm->pExpr = p;
pTerm->flags = flags;
pTerm->pWC = pWC;
pTerm->iPartner = -1;
return pTerm;
}
/*
** This routine identifies subexpressions in the WHERE clause where
** each subexpression is separate by the AND operator. aSlot is
** filled with pointers to the subexpressions. For example:
**
** WHERE a=='hello' AND coalesce(b,11)<10 AND (c+12!=d OR c==22)
** \________/ \_______________/ \________________/
** slot[0] slot[1] slot[2]
**
** The original WHERE clause in pExpr is unaltered. All this routine
** does is make aSlot[] entries point to substructure within pExpr.
**
** aSlot[] is an array of subexpressions structures. There are nSlot
** spaces left in this array. This routine finds as many AND-separated
** subexpressions as it can and puts pointers to those subexpressions
** into aSlot[] entries. The return value is the number of slots filled.
*/
static void whereSplit(WhereClause *pWC, Expr *pExpr){
if( pExpr==0 ) return;
if( pExpr->op!=TK_AND ){
whereClauseInsert(pWC, pExpr, 0);
}else{
whereSplit(pWC, pExpr->pLeft);
whereSplit(pWC, pExpr->pRight);
}
}
/*
** Initialize an expression mask set
*/
#define initMaskSet(P) memset(P, 0, sizeof(*P))
/*
** Return the bitmask for the given cursor number. Return 0 if
** iCursor is not in the set.
*/
static Bitmask getMask(ExprMaskSet *pMaskSet, int iCursor){
int i;
for(i=0; i<pMaskSet->n; i++){
if( pMaskSet->ix[i]==iCursor ){
return ((Bitmask)1)<<i;
}
}
return 0;
}
/*
** Create a new mask for cursor iCursor.
**
** There is one cursor per table in the FROM clause. The number of
** tables in the FROM clause is limited by a test early in the
** sqlite3WhereBegin() routien. So we know that the pMaskSet->ix[]
** array will never overflow.
*/
static void createMask(ExprMaskSet *pMaskSet, int iCursor){
assert( pMaskSet->n < ARRAYSIZE(pMaskSet->ix) );
pMaskSet->ix[pMaskSet->n++] = iCursor;
}
/*
** Destroy an expression mask set
*/
#define freeMaskSet(P) /* NO-OP */
/*
** This routine walks (recursively) an expression tree and generates
** a bitmask indicating which tables are used in that expression
** tree.
**
** In order for this routine to work, the calling function must have
** previously invoked sqlite3ExprResolveNames() on the expression. See
** the header comment on that routine for additional information.
** The sqlite3ExprResolveNames() routines looks for column names and
** sets their opcodes to TK_COLUMN and their Expr.iTable fields to
** the VDBE cursor number of the table.
*/
static Bitmask exprListTableUsage(ExprMaskSet *, ExprList *);
static Bitmask exprTableUsage(ExprMaskSet *pMaskSet, Expr *p){
Bitmask mask = 0;
if( p==0 ) return 0;
if( p->op==TK_COLUMN ){
mask = getMask(pMaskSet, p->iTable);
return mask;
}
mask = exprTableUsage(pMaskSet, p->pRight);
mask |= exprTableUsage(pMaskSet, p->pLeft);
mask |= exprListTableUsage(pMaskSet, p->pList);
if( p->pSelect ){
Select *pS = p->pSelect;
mask |= exprListTableUsage(pMaskSet, pS->pEList);
mask |= exprListTableUsage(pMaskSet, pS->pGroupBy);
mask |= exprListTableUsage(pMaskSet, pS->pOrderBy);
mask |= exprTableUsage(pMaskSet, pS->pWhere);
mask |= exprTableUsage(pMaskSet, pS->pHaving);
}
return mask;
}
static Bitmask exprListTableUsage(ExprMaskSet *pMaskSet, ExprList *pList){
int i;
Bitmask mask = 0;
if( pList ){
for(i=0; i<pList->nExpr; i++){
mask |= exprTableUsage(pMaskSet, pList->a[i].pExpr);
}
}
return mask;
}
/*
** Return TRUE if the given operator is one of the operators that is
** allowed for an indexable WHERE clause term. The allowed operators are
** "=", "<", ">", "<=", ">=", and "IN".
*/
static int allowedOp(int op){
assert( TK_GT==TK_LE-1 && TK_LE==TK_LT-1 && TK_LT==TK_GE-1 && TK_EQ==TK_GT-1);
return op==TK_IN || (op>=TK_EQ && op<=TK_GE);
}
/*
** Swap two objects of type T.
*/
#define SWAP(TYPE,A,B) {TYPE t=A; A=B; B=t;}
/*
** Commute a comparision operator. Expressions of the form "X op Y"
** are converted into "Y op X".
*/
static void exprCommute(Expr *pExpr){
assert(
pExpr->op==TK_EQ ||
pExpr->op==TK_NE ||
pExpr->op==TK_LT ||
pExpr->op==TK_LE ||
pExpr->op==TK_GT ||
pExpr->op==TK_GE
);
SWAP(CollSeq*,pExpr->pRight->pColl,pExpr->pLeft->pColl);
SWAP(Expr*,pExpr->pRight,pExpr->pLeft);
if( pExpr->op>=TK_GT ){
assert( TK_LT==TK_GT+2 );
assert( TK_GE==TK_LE+2 );
assert( TK_GT>TK_EQ );
assert( TK_GT<TK_LE );
assert( pExpr->op>=TK_GT && pExpr->op<=TK_GE );
pExpr->op = ((pExpr->op-TK_GT)^2)+TK_GT;
}
}
/*
** The input to this routine is an WhereTerm structure with only the
** "p" field filled in. The job of this routine is to analyze the
** subexpression and populate all the other fields of the WhereTerm
** structure.
*/
static void exprAnalyze(
SrcList *pSrc, /* the FROM clause */
ExprMaskSet *pMaskSet, /* table masks */
WhereTerm *pTerm /* the WHERE clause term to be analyzed */
){
Expr *pExpr = pTerm->pExpr;
Bitmask prereqLeft;
Bitmask prereqAll;
int idxRight;
prereqLeft = exprTableUsage(pMaskSet, pExpr->pLeft);
pTerm->prereqRight = exprTableUsage(pMaskSet, pExpr->pRight);
pTerm->prereqAll = prereqAll = exprTableUsage(pMaskSet, pExpr);
pTerm->leftCursor = -1;
pTerm->iPartner = -1;
idxRight = -1;
if( allowedOp(pExpr->op) && (pTerm->prereqRight & prereqLeft)==0 ){
Expr *pLeft = pExpr->pLeft;
Expr *pRight = pExpr->pRight;
if( pLeft->op==TK_COLUMN ){
pTerm->leftCursor = pLeft->iTable;
pTerm->leftColumn = pLeft->iColumn;
}
if( pRight && pRight->op==TK_COLUMN ){
WhereTerm *pNew;
Expr *pDup;
if( pTerm->leftCursor>=0 ){
pDup = sqlite3ExprDup(pExpr);
pNew = whereClauseInsert(pTerm->pWC, pDup, TERM_VIRTUAL|TERM_DYNAMIC);
if( pNew==0 ) return;
pNew->iPartner = pTerm->idx;
}else{
pDup = pExpr;
pNew = pTerm;
}
exprCommute(pDup);
pLeft = pDup->pLeft;
pNew->leftCursor = pLeft->iTable;
pNew->leftColumn = pLeft->iColumn;
pNew->prereqRight = prereqLeft;
pNew->prereqAll = prereqAll;
}
}
}
/*
** This routine decides if pIdx can be used to satisfy the ORDER BY
** clause. If it can, it returns 1. If pIdx cannot satisfy the
** ORDER BY clause, this routine returns 0.
**
** pOrderBy is an ORDER BY clause from a SELECT statement. pTab is the
** left-most table in the FROM clause of that same SELECT statement and
** the table has a cursor number of "base". pIdx is an index on pTab.
**
** nEqCol is the number of columns of pIdx that are used as equality
** constraints. Any of these columns may be missing from the ORDER BY
** clause and the match can still be a success.
**
** If the index is UNIQUE, then the ORDER BY clause is allowed to have
** additional terms past the end of the index and the match will still
** be a success.
**
** All terms of the ORDER BY that match against the index must be either
** ASC or DESC. (Terms of the ORDER BY clause past the end of a UNIQUE
** index do not need to satisfy this constraint.) The *pbRev value is
** set to 1 if the ORDER BY clause is all DESC and it is set to 0 if
** the ORDER BY clause is all ASC.
*/
static int isSortingIndex(
Parse *pParse, /* Parsing context */
Index *pIdx, /* The index we are testing */
Table *pTab, /* The table to be sorted */
int base, /* Cursor number for pTab */
ExprList *pOrderBy, /* The ORDER BY clause */
int nEqCol, /* Number of index columns with == constraints */
int *pbRev /* Set to 1 if ORDER BY is DESC */
){
int i, j; /* Loop counters */
int sortOrder; /* Which direction we are sorting */
int nTerm; /* Number of ORDER BY terms */
struct ExprList_item *pTerm; /* A term of the ORDER BY clause */
sqlite3 *db = pParse->db;
assert( pOrderBy!=0 );
nTerm = pOrderBy->nExpr;
assert( nTerm>0 );
/* Match terms of the ORDER BY clause against columns of
** the index.
*/
for(i=j=0, pTerm=pOrderBy->a; j<nTerm && i<pIdx->nColumn; i++){
Expr *pExpr; /* The expression of the ORDER BY pTerm */
CollSeq *pColl; /* The collating sequence of pExpr */
pExpr = pTerm->pExpr;
if( pExpr->op!=TK_COLUMN || pExpr->iTable!=base ){
/* Can not use an index sort on anything that is not a column in the
** left-most table of the FROM clause */
return 0;
}
pColl = sqlite3ExprCollSeq(pParse, pExpr);
if( !pColl ) pColl = db->pDfltColl;
if( pExpr->iColumn!=pIdx->aiColumn[i] || pColl!=pIdx->keyInfo.aColl[i] ){
/* Term j of the ORDER BY clause does not match column i of the index */
if( i<nEqCol ){
/* If an index column that is constrained by == fails to match an
** ORDER BY term, that is OK. Just ignore that column of the index
*/
continue;
}else{
/* If an index column fails to match and is not constrained by ==
** then the index cannot satisfy the ORDER BY constraint.
*/
return 0;
}
}
if( i>nEqCol ){
if( pTerm->sortOrder!=sortOrder ){
/* Indices can only be used if all ORDER BY terms past the
** equality constraints are all either DESC or ASC. */
return 0;
}
}else{
sortOrder = pTerm->sortOrder;
}
j++;
pTerm++;
}
/* The index can be used for sorting if all terms of the ORDER BY clause
** or covered or if we ran out of index columns and the it is a UNIQUE
** index.
*/
if( j>=nTerm || (i>=pIdx->nColumn && pIdx->onError!=OE_None) ){
*pbRev = sortOrder==SQLITE_SO_DESC;
return 1;
}
return 0;
}
/*
** Check table to see if the ORDER BY clause in pOrderBy can be satisfied
** by sorting in order of ROWID. Return true if so and set *pbRev to be
** true for reverse ROWID and false for forward ROWID order.
*/
static int sortableByRowid(
int base, /* Cursor number for table to be sorted */
ExprList *pOrderBy, /* The ORDER BY clause */
int *pbRev /* Set to 1 if ORDER BY is DESC */
){
Expr *p;
assert( pOrderBy!=0 );
assert( pOrderBy->nExpr>0 );
p = pOrderBy->a[0].pExpr;
if( p->op==TK_COLUMN && p->iTable==base && p->iColumn==-1 ){
*pbRev = pOrderBy->a[0].sortOrder;
return 1;
}
return 0;
}
/*
** Disable a term in the WHERE clause. Except, do not disable the term
** if it controls a LEFT OUTER JOIN and it did not originate in the ON
** or USING clause of that join.
**
** Consider the term t2.z='ok' in the following queries:
**
** (1) SELECT * FROM t1 LEFT JOIN t2 ON t1.a=t2.x WHERE t2.z='ok'
** (2) SELECT * FROM t1 LEFT JOIN t2 ON t1.a=t2.x AND t2.z='ok'
** (3) SELECT * FROM t1, t2 WHERE t1.a=t2.x AND t2.z='ok'
**
** The t2.z='ok' is disabled in the in (2) because it originates
** in the ON clause. The term is disabled in (3) because it is not part
** of a LEFT OUTER JOIN. In (1), the term is not disabled.
**
** Disabling a term causes that term to not be tested in the inner loop
** of the join. Disabling is an optimization. We would get the correct
** results if nothing were ever disabled, but joins might run a little
** slower. The trick is to disable as much as we can without disabling
** too much. If we disabled in (1), we'd get the wrong answer.
** See ticket #813.
*/
static void disableTerm(WhereLevel *pLevel, WhereTerm *pTerm){
if( pTerm
&& (pTerm->flags & TERM_CODED)==0
&& (pLevel->iLeftJoin==0 || ExprHasProperty(pTerm->pExpr, EP_FromJoin))
){
pTerm->flags |= TERM_CODED;
if( pTerm->iPartner>=0 ){
disableTerm(pLevel, &pTerm->pWC->a[pTerm->iPartner]);
}
}
}
/*
** Generate code that builds a probe for an index. Details:
**
** * Check the top nColumn entries on the stack. If any
** of those entries are NULL, jump immediately to brk,
** which is the loop exit, since no index entry will match
** if any part of the key is NULL.
**
** * Construct a probe entry from the top nColumn entries in
** the stack with affinities appropriate for index pIdx.
*/
static void buildIndexProbe(Vdbe *v, int nColumn, int brk, Index *pIdx){
sqlite3VdbeAddOp(v, OP_NotNull, -nColumn, sqlite3VdbeCurrentAddr(v)+3);
sqlite3VdbeAddOp(v, OP_Pop, nColumn, 0);
sqlite3VdbeAddOp(v, OP_Goto, 0, brk);
sqlite3VdbeAddOp(v, OP_MakeRecord, nColumn, 0);
sqlite3IndexAffinityStr(v, pIdx);
}
/*
** Search for a term in the WHERE clause that is of the form "X <op> <expr>"
** where X is a reference to the iColumn of table iCur and <op> is either
** op1 or op2. Return a pointer to the term.
*/
static WhereTerm *findTerm(
WhereClause *pWC, /* The WHERE clause to be searched */
int iCur, /* Cursor number of LHS */
int iColumn, /* Column number of LHS */
Bitmask loopMask, /* RHS must not overlap with this mask */
u8 op1, u8 op2 /* Expression must use either of these opcodes */
){
WhereTerm *pTerm;
int k;
for(pTerm=pWC->a, k=pWC->nTerm; k; k--, pTerm++){
u8 op = pTerm->pExpr->op;
if( pTerm->leftCursor==iCur
&& (pTerm->prereqRight & loopMask)==0
&& pTerm->leftColumn==iColumn
&& (op==op1 || op==op2)
){
break;
}
}
assert( k>0 ); /* The search is always successful */
return pTerm;
}
/*
** Generate code for an equality term of the WHERE clause. An equality
** term can be either X=expr or X IN (...). pTerm is the X.
*/
static void codeEqualityTerm(
Parse *pParse, /* The parsing context */
WhereTerm *pTerm, /* The term of the WHERE clause to be coded */
int brk, /* Jump here to abandon the loop */
WhereLevel *pLevel /* When level of the FROM clause we are working on */
){
Expr *pX = pTerm->pExpr;
if( pX->op!=TK_IN ){
assert( pX->op==TK_EQ );
sqlite3ExprCode(pParse, pX->pRight);
#ifndef SQLITE_OMIT_SUBQUERY
}else{
int iTab;
Vdbe *v = pParse->pVdbe;
sqlite3CodeSubselect(pParse, pX);
iTab = pX->iTable;
sqlite3VdbeAddOp(v, OP_Rewind, iTab, brk);
VdbeComment((v, "# %.*s", pX->span.n, pX->span.z));
pLevel->inP2 = sqlite3VdbeAddOp(v, OP_Column, iTab, 0);
pLevel->inOp = OP_Next;
pLevel->inP1 = iTab;
#endif
}
disableTerm(pLevel, pTerm);
}
#ifdef SQLITE_TEST
/*
** The following variable holds a text description of query plan generated
** by the most recent call to sqlite3WhereBegin(). Each call to WhereBegin
** overwrites the previous. This information is used for testing and
** analysis only.
*/
char sqlite3_query_plan[BMS*2*40]; /* Text of the join */
static int nQPlan = 0; /* Next free slow in _query_plan[] */
#endif /* SQLITE_TEST */
/*
** Generate the beginning of the loop used for WHERE clause processing.
** The return value is a pointer to an opaque structure that contains
** information needed to terminate the loop. Later, the calling routine
** should invoke sqlite3WhereEnd() with the return value of this function
** in order to complete the WHERE clause processing.
**
** If an error occurs, this routine returns NULL.
**
** The basic idea is to do a nested loop, one loop for each table in
** the FROM clause of a select. (INSERT and UPDATE statements are the
** same as a SELECT with only a single table in the FROM clause.) For
** example, if the SQL is this:
**
** SELECT * FROM t1, t2, t3 WHERE ...;
**
** Then the code generated is conceptually like the following:
**
** foreach row1 in t1 do \ Code generated
** foreach row2 in t2 do |-- by sqlite3WhereBegin()
** foreach row3 in t3 do /
** ...
** end \ Code generated
** end |-- by sqlite3WhereEnd()
** end /
**
** There are Btree cursors associated with each table. t1 uses cursor
** number pTabList->a[0].iCursor. t2 uses the cursor pTabList->a[1].iCursor.
** And so forth. This routine generates code to open those VDBE cursors
** and sqlite3WhereEnd() generates the code to close them.
**
** The code that sqlite3WhereBegin() generates leaves the cursors named
** in pTabList pointing at their appropriate entries. The [...] code
** can use OP_Column and OP_Rowid opcodes on these cursors to extract
** data from the various tables of the loop.
**
** If the WHERE clause is empty, the foreach loops must each scan their
** entire tables. Thus a three-way join is an O(N^3) operation. But if
** the tables have indices and there are terms in the WHERE clause that
** refer to those indices, a complete table scan can be avoided and the
** code will run much faster. Most of the work of this routine is checking
** to see if there are indices that can be used to speed up the loop.
**
** Terms of the WHERE clause are also used to limit which rows actually
** make it to the "..." in the middle of the loop. After each "foreach",
** terms of the WHERE clause that use only terms in that loop and outer
** loops are evaluated and if false a jump is made around all subsequent
** inner loops (or around the "..." if the test occurs within the inner-
** most loop)
**
** OUTER JOINS
**
** An outer join of tables t1 and t2 is conceptally coded as follows:
**
** foreach row1 in t1 do
** flag = 0
** foreach row2 in t2 do
** start:
** ...
** flag = 1
** end
** if flag==0 then
** move the row2 cursor to a null row
** goto start
** fi
** end
**
** ORDER BY CLAUSE PROCESSING
**
** *ppOrderBy is a pointer to the ORDER BY clause of a SELECT statement,
** if there is one. If there is no ORDER BY clause or if this routine
** is called from an UPDATE or DELETE statement, then ppOrderBy is NULL.
**
** If an index can be used so that the natural output order of the table
** scan is correct for the ORDER BY clause, then that index is used and
** *ppOrderBy is set to NULL. This is an optimization that prevents an
** unnecessary sort of the result set if an index appropriate for the
** ORDER BY clause already exists.
**
** If the where clause loops cannot be arranged to provide the correct
** output order, then the *ppOrderBy is unchanged.
*/
WhereInfo *sqlite3WhereBegin(
Parse *pParse, /* The parser context */
SrcList *pTabList, /* A list of all tables to be scanned */
Expr *pWhere, /* The WHERE clause */
ExprList **ppOrderBy /* An ORDER BY clause, or NULL */
){
int i; /* Loop counter */
WhereInfo *pWInfo; /* Will become the return value of this function */
Vdbe *v = pParse->pVdbe; /* The virtual database engine */
int brk, cont = 0; /* Addresses used during code generation */
Bitmask loopMask; /* One bit cleared for each outer loop */
WhereTerm *pTerm; /* A single term in the WHERE clause */
ExprMaskSet maskSet; /* The expression mask set */
int iDirectEq[BMS]; /* Term of the form ROWID==X for the N-th table */
int iDirectLt[BMS]; /* Term of the form ROWID<X or ROWID<=X */
int iDirectGt[BMS]; /* Term of the form ROWID>X or ROWID>=X */
WhereClause wc; /* The WHERE clause is divided into these terms */
struct SrcList_item *pTabItem; /* A single entry from pTabList */
WhereLevel *pLevel; /* A single level in the pWInfo list */
/* The number of terms in the FROM clause is limited by the number of
** bits in a Bitmask
*/
if( pTabList->nSrc>sizeof(Bitmask)*8 ){
sqlite3ErrorMsg(pParse, "at most %d tables in a join",
sizeof(Bitmask)*8);
return 0;
}
/* Split the WHERE clause into separate subexpressions where each
** subexpression is separated by an AND operator. If the wc.a[]
** array fills up, the last entry might point to an expression which
** contains additional unfactored AND operators.
*/
initMaskSet(&maskSet);
whereClauseInit(&wc);
whereSplit(&wc, pWhere);
/* Allocate and initialize the WhereInfo structure that will become the
** return value.
*/
pWInfo = sqliteMalloc( sizeof(WhereInfo) + pTabList->nSrc*sizeof(WhereLevel));
if( sqlite3_malloc_failed ){
sqliteFree(pWInfo); /* Avoid leaking memory when malloc fails */
whereClauseClear(&wc);
return 0;
}
pWInfo->pParse = pParse;
pWInfo->pTabList = pTabList;
pWInfo->iBreak = sqlite3VdbeMakeLabel(v);
/* Special case: a WHERE clause that is constant. Evaluate the
** expression and either jump over all of the code or fall thru.
*/
if( pWhere && (pTabList->nSrc==0 || sqlite3ExprIsConstant(pWhere)) ){
sqlite3ExprIfFalse(pParse, pWhere, pWInfo->iBreak, 1);
pWhere = 0;
}
/* Analyze all of the subexpressions.
*/
for(i=0; i<pTabList->nSrc; i++){
createMask(&maskSet, pTabList->a[i].iCursor);
}
for(i=wc.nTerm-1; i>=0; i--){
exprAnalyze(pTabList, &maskSet, &wc.a[i]);
}
/* Figure out what index to use (if any) for each nested loop.
** Make pWInfo->a[i].pIdx point to the index to use for the i-th nested
** loop where i==0 is the outer loop and i==pTabList->nSrc-1 is the inner
** loop.
**
** If terms exist that use the ROWID of any table, then set the
** iDirectEq[], iDirectLt[], or iDirectGt[] elements for that table
** to the index of the term containing the ROWID. We always prefer
** to use a ROWID which can directly access a table rather than an
** index which requires reading an index first to get the rowid then
** doing a second read of the actual database table.
**
** Actually, if there are more than 32 tables in the join, only the
** first 32 tables are candidates for indices. This is (again) due
** to the limit of 32 bits in an integer bitmask.
*/
loopMask = ~(Bitmask)0;
pTabItem = pTabList->a;
pLevel = pWInfo->a;
for(i=0; i<pTabList->nSrc && i<ARRAYSIZE(iDirectEq); i++,pTabItem++,pLevel++){
int j;
int iCur = pTabItem->iCursor; /* The cursor for this table */
Bitmask mask = getMask(&maskSet, iCur); /* Cursor mask for this table */
Table *pTab = pTabItem->pTab;
Index *pIdx;
Index *pBestIdx = 0;
int bestScore = 0;
int bestRev = 0;
/* Check to see if there is an expression that uses only the
** ROWID field of this table. For terms of the form ROWID==expr
** set iDirectEq[i] to the index of the term. For terms of the
** form ROWID<expr or ROWID<=expr set iDirectLt[i] to the term index.
** For terms like ROWID>expr or ROWID>=expr set iDirectGt[i].
**
** (Added:) Treat ROWID IN expr like ROWID=expr.
*/
pLevel->iIdxCur = -1;
iDirectEq[i] = -1;
iDirectLt[i] = -1;
iDirectGt[i] = -1;
for(pTerm=wc.a, j=0; j<wc.nTerm; j++, pTerm++){
if( pTerm->leftCursor==iCur && pTerm->leftColumn<0
&& (pTerm->prereqRight & loopMask)==0 ){
switch( pTerm->pExpr->op ){
case TK_IN:
case TK_EQ: iDirectEq[i] = j; break;
case TK_LE:
case TK_LT: iDirectLt[i] = j; break;
case TK_GE:
case TK_GT: iDirectGt[i] = j; break;
}
}
}
/* If we found a term that tests ROWID with == or IN, that term
** will be used to locate the rows in the database table. There
** is no need to continue into the code below that looks for
** an index. We will always use the ROWID over an index.
*/
if( iDirectEq[i]>=0 ){
loopMask &= ~mask;
pLevel->pIdx = 0;
continue;
}
/* Do a search for usable indices. Leave pBestIdx pointing to
** the "best" index. pBestIdx is left set to NULL if no indices
** are usable.
**
** The best index is the one with the highest score. The score
** for the index is determined as follows. For each of the
** left-most terms that is fixed by an equality operator, add
** 32 to the score. The right-most term of the index may be
** constrained by an inequality. Add 4 if for an "x<..." constraint
** and add 8 for an "x>..." constraint. If both constraints
** are present, add 12.
**
** If the left-most term of the index uses an IN operator
** (ex: "x IN (...)") then add 16 to the score.
**
** If an index can be used for sorting, add 2 to the score.
** If an index contains all the terms of a table that are ever
** used by any expression in the SQL statement, then add 1 to
** the score.
**
** This scoring system is designed so that the score can later be
** used to determine how the index is used. If the score&0x1c is 0
** then all constraints are equalities. If score&0x4 is not 0 then
** there is an inequality used as a termination key. (ex: "x<...")
** If score&0x8 is not 0 then there is an inequality used as the
** start key. (ex: "x>..."). A score or 0x10 is the special case
** of an IN operator constraint. (ex: "x IN ...").
**
** The IN operator (as in "<expr> IN (...)") is treated the same as
** an equality comparison except that it can only be used on the
** left-most column of an index and other terms of the WHERE clause
** cannot be used in conjunction with the IN operator to help satisfy
** other columns of the index.
*/
for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
Bitmask eqMask = 0; /* Index columns covered by an x=... term */
Bitmask ltMask = 0; /* Index columns covered by an x<... term */
Bitmask gtMask = 0; /* Index columns covered by an x>... term */
Bitmask inMask = 0; /* Index columns covered by an x IN .. term */
Bitmask m;
int nEq, score, bRev = 0;
if( pIdx->nColumn>sizeof(eqMask)*8 ){
continue; /* Ignore indices with too many columns to analyze */
}
for(pTerm=wc.a, j=0; j<wc.nTerm; j++, pTerm++){
Expr *pX = pTerm->pExpr;
CollSeq *pColl = sqlite3ExprCollSeq(pParse, pX->pLeft);
if( !pColl && pX->pRight ){
pColl = sqlite3ExprCollSeq(pParse, pX->pRight);
}
if( !pColl ){
pColl = pParse->db->pDfltColl;
}
if( pTerm->leftCursor==iCur && (pTerm->prereqRight & loopMask)==0 ){
int iColumn = pTerm->leftColumn;
int k;
char idxaff = iColumn>=0 ? pIdx->pTable->aCol[iColumn].affinity : 0;
for(k=0; k<pIdx->nColumn; k++){
/* If the collating sequences or affinities don't match,
** ignore this index. */
if( pColl!=pIdx->keyInfo.aColl[k] ) continue;
if( !sqlite3IndexAffinityOk(pX, idxaff) ) continue;
if( pIdx->aiColumn[k]==iColumn ){
switch( pX->op ){
case TK_IN: {
if( k==0 ) inMask |= 1;
break;
}
case TK_EQ: {
eqMask |= ((Bitmask)1)<<k;
break;
}
case TK_LE:
case TK_LT: {
ltMask |= ((Bitmask)1)<<k;
break;
}
case TK_GE:
case TK_GT: {
gtMask |= ((Bitmask)1)<<k;
break;
}
default: {
/* CANT_HAPPEN */
assert( 0 );
break;
}
}
break;
}
}
}
}
/* The following loop ends with nEq set to the number of columns
** on the left of the index with == constraints.
*/
for(nEq=0; nEq<pIdx->nColumn; nEq++){
m = (((Bitmask)1)<<(nEq+1))-1;
if( (m & eqMask)!=m ) break;
}
/* Begin assembling the score
*/
score = nEq*32; /* Base score is 32 times number of == constraints */
m = ((Bitmask)1)<<nEq;
if( m & ltMask ) score+=4; /* Increase score for a < constraint */
if( m & gtMask ) score+=8; /* Increase score for a > constraint */
if( score==0 && inMask ) score = 16; /* Default score for IN constraint */
/* Give bonus points if this index can be used for sorting
*/
if( i==0 && score!=16 && ppOrderBy && *ppOrderBy ){
int base = pTabList->a[0].iCursor;
if( isSortingIndex(pParse, pIdx, pTab, base, *ppOrderBy, nEq, &bRev) ){
score += 2;
}
}
/* Check to see if we can get away with using just the index without
** ever reading the table. If that is the case, then add one bonus
** point to the score.
*/
if( score && pTabItem->colUsed < (((Bitmask)1)<<(BMS-1)) ){
for(m=0, j=0; j<pIdx->nColumn; j++){
int x = pIdx->aiColumn[j];
if( x<BMS-1 ){
m |= ((Bitmask)1)<<x;
}
}
if( (pTabItem->colUsed & m)==pTabItem->colUsed ){
score++;
}
}
/* If the score for this index is the best we have seen so far, then
** save it
*/
if( score>bestScore ){
pBestIdx = pIdx;
bestScore = score;
bestRev = bRev;
}
}
pLevel->pIdx = pBestIdx;
pLevel->score = bestScore;
pLevel->bRev = bestRev;
loopMask &= ~mask;
if( pBestIdx ){
pLevel->iIdxCur = pParse->nTab++;
}
}
/* Check to see if the ORDER BY clause is or can be satisfied by the
** use of an index on the first table.
*/
if( ppOrderBy && *ppOrderBy && pTabList->nSrc>0 ){
Index *pIdx; /* Index derived from the WHERE clause */
Table *pTab; /* Left-most table in the FROM clause */
int bRev = 0; /* True to reverse the output order */
int iCur; /* Btree-cursor that will be used by pTab */
WhereLevel *pLevel0 = &pWInfo->a[0];
pTab = pTabList->a[0].pTab;
pIdx = pLevel0->pIdx;
iCur = pTabList->a[0].iCursor;
if( pIdx==0 && sortableByRowid(iCur, *ppOrderBy, &bRev) ){
/* The ORDER BY clause specifies ROWID order, which is what we
** were going to be doing anyway...
*/
*ppOrderBy = 0;
pLevel0->bRev = bRev;
}else if( pLevel0->score==16 ){
/* If there is already an IN index on the left-most table,
** it will not give the correct sort order.
** So, pretend that no suitable index is found.
*/
}else if( iDirectEq[0]>=0 || iDirectLt[0]>=0 || iDirectGt[0]>=0 ){
/* If the left-most column is accessed using its ROWID, then do
** not try to sort by index. But do delete the ORDER BY clause
** if it is redundant.
*/
}else if( (pLevel0->score&2)!=0 ){
/* The index that was selected for searching will cause rows to
** appear in sorted order.
*/
*ppOrderBy = 0;
}
}
/* Open all tables in the pTabList and any indices selected for
** searching those tables.
*/
sqlite3CodeVerifySchema(pParse, -1); /* Insert the cookie verifier Goto */
pLevel = pWInfo->a;
for(i=0, pTabItem=pTabList->a; i<pTabList->nSrc; i++, pTabItem++, pLevel++){
Table *pTab;
Index *pIx;
int iIdxCur = pLevel->iIdxCur;
pTab = pTabItem->pTab;
if( pTab->isTransient || pTab->pSelect ) continue;
if( (pLevel->score & 1)==0 ){
sqlite3OpenTableForReading(v, pTabItem->iCursor, pTab);
}
pLevel->iTabCur = pTabItem->iCursor;
if( (pIx = pLevel->pIdx)!=0 ){
sqlite3VdbeAddOp(v, OP_Integer, pIx->iDb, 0);
sqlite3VdbeOp3(v, OP_OpenRead, iIdxCur, pIx->tnum,
(char*)&pIx->keyInfo, P3_KEYINFO);
}
if( (pLevel->score & 1)!=0 ){
sqlite3VdbeAddOp(v, OP_SetNumColumns, iIdxCur, pIx->nColumn+1);
}
sqlite3CodeVerifySchema(pParse, pTab->iDb);
#ifdef SQLITE_TEST
/* Record in the query plan information about the current table
** and the index used to access it (if any). If the table itself
** is not used, its name is just '{}'. If no index is used
** the index is listed as "{}"
*/
{
char *z = pTabItem->zAlias;
int n;
if( z==0 ) z = pTab->zName;
n = strlen(z);
if( n+nQPlan < sizeof(sqlite3_query_plan)-10 ){
if( (pLevel->score & 1)!=0 ){
strcpy(&sqlite3_query_plan[nQPlan], "{}");
nQPlan += 2;
}else{
strcpy(&sqlite3_query_plan[nQPlan], z);
nQPlan += n;
}
sqlite3_query_plan[nQPlan++] = ' ';
}
if( pIx==0 ){
strcpy(&sqlite3_query_plan[nQPlan], " {}");
nQPlan += 3;
}else{
n = strlen(pIx->zName);
if( n+nQPlan < sizeof(sqlite3_query_plan)-2 ){
strcpy(&sqlite3_query_plan[nQPlan], pIx->zName);
nQPlan += n;
sqlite3_query_plan[nQPlan++] = ' ';
}
}
}
#endif
}
pWInfo->iTop = sqlite3VdbeCurrentAddr(v);
#ifdef SQLITE_TEST
/* Terminate the query plan description
*/
while( nQPlan>0 && sqlite3_query_plan[nQPlan-1]==' ' ){
sqlite3_query_plan[--nQPlan] = 0;
}
sqlite3_query_plan[nQPlan] = 0;
nQPlan = 0;
#endif
/* Generate the code to do the search
*/
loopMask = ~(Bitmask)0;
pLevel = pWInfo->a;
pTabItem = pTabList->a;
for(i=0; i<pTabList->nSrc; i++, pTabItem++, pLevel++){
int j, k;
int iCur = pTabItem->iCursor; /* The VDBE cursor for the table */
Index *pIdx; /* The index we will be using */
int iIdxCur; /* The VDBE cursor for the index */
int omitTable; /* True if we use the index only */
pIdx = pLevel->pIdx;
iIdxCur = pLevel->iIdxCur;
pLevel->inOp = OP_Noop;
/* Check to see if it is appropriate to omit the use of the table
** here and use its index instead.
*/
omitTable = (pLevel->score&1)!=0;
/* If this is the right table of a LEFT OUTER JOIN, allocate and
** initialize a memory cell that records if this table matches any
** row of the left table of the join.
*/
if( i>0 && (pTabList->a[i-1].jointype & JT_LEFT)!=0 ){
if( !pParse->nMem ) pParse->nMem++;
pLevel->iLeftJoin = pParse->nMem++;
sqlite3VdbeAddOp(v, OP_Null, 0, 0);
sqlite3VdbeAddOp(v, OP_MemStore, pLevel->iLeftJoin, 1);
VdbeComment((v, "# init LEFT JOIN no-match flag"));
}
if( i<ARRAYSIZE(iDirectEq) && (k = iDirectEq[i])>=0 ){
/* Case 1: We can directly reference a single row using an
** equality comparison against the ROWID field. Or
** we reference multiple rows using a "rowid IN (...)"
** construct.
*/
assert( k<wc.nTerm );
pTerm = &wc.a[k];
assert( pTerm->pExpr!=0 );
assert( pTerm->leftCursor==iCur );
assert( omitTable==0 );
brk = pLevel->brk = sqlite3VdbeMakeLabel(v);
codeEqualityTerm(pParse, pTerm, brk, pLevel);
cont = pLevel->cont = sqlite3VdbeMakeLabel(v);
sqlite3VdbeAddOp(v, OP_MustBeInt, 1, brk);
sqlite3VdbeAddOp(v, OP_NotExists, iCur, brk);
VdbeComment((v, "pk"));
pLevel->op = OP_Noop;
}else if( pIdx!=0 && pLevel->score>3 && (pLevel->score&0x0c)==0 ){
/* Case 2: There is an index and all terms of the WHERE clause that
** refer to the index using the "==" or "IN" operators.
*/
int start;
int nColumn = (pLevel->score+16)/32;
brk = pLevel->brk = sqlite3VdbeMakeLabel(v);
/* For each column of the index, find the term of the WHERE clause that
** constraints that column. If the WHERE clause term is X=expr, then
** generate code to evaluate expr and leave the result on the stack */
for(j=0; j<nColumn; j++){
pTerm = findTerm(&wc, iCur, pIdx->aiColumn[j], loopMask, TK_EQ, TK_IN);
assert( pTerm!=0 );
assert( (pTerm->flags & TERM_CODED)==0 );
codeEqualityTerm(pParse, pTerm, brk, pLevel);
}
pLevel->iMem = pParse->nMem++;
cont = pLevel->cont = sqlite3VdbeMakeLabel(v);
buildIndexProbe(v, nColumn, brk, pIdx);
sqlite3VdbeAddOp(v, OP_MemStore, pLevel->iMem, 0);
/* Generate code (1) to move to the first matching element of the table.
** Then generate code (2) that jumps to "brk" after the cursor is past
** the last matching element of the table. The code (1) is executed
** once to initialize the search, the code (2) is executed before each
** iteration of the scan to see if the scan has finished. */
if( pLevel->bRev ){
/* Scan in reverse order */
sqlite3VdbeAddOp(v, OP_MoveLe, iIdxCur, brk);
start = sqlite3VdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
sqlite3VdbeAddOp(v, OP_IdxLT, iIdxCur, brk);
pLevel->op = OP_Prev;
}else{
/* Scan in the forward order */
sqlite3VdbeAddOp(v, OP_MoveGe, iIdxCur, brk);
start = sqlite3VdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
sqlite3VdbeOp3(v, OP_IdxGE, iIdxCur, brk, "+", P3_STATIC);
pLevel->op = OP_Next;
}
sqlite3VdbeAddOp(v, OP_RowKey, iIdxCur, 0);
sqlite3VdbeAddOp(v, OP_IdxIsNull, nColumn, cont);
if( !omitTable ){
sqlite3VdbeAddOp(v, OP_IdxRowid, iIdxCur, 0);
sqlite3VdbeAddOp(v, OP_MoveGe, iCur, 0);
}
pLevel->p1 = iIdxCur;
pLevel->p2 = start;
}else if( i<ARRAYSIZE(iDirectLt) && (iDirectLt[i]>=0 || iDirectGt[i]>=0) ){
/* Case 3: We have an inequality comparison against the ROWID field.
*/
int testOp = OP_Noop;
int start;
int bRev = pLevel->bRev;
assert( omitTable==0 );
brk = pLevel->brk = sqlite3VdbeMakeLabel(v);
cont = pLevel->cont = sqlite3VdbeMakeLabel(v);
if( bRev ){
int t = iDirectGt[i];
iDirectGt[i] = iDirectLt[i];
iDirectLt[i] = t;
}
if( iDirectGt[i]>=0 ){
Expr *pX;
k = iDirectGt[i];
assert( k<wc.nTerm );
pTerm = &wc.a[k];
pX = pTerm->pExpr;
assert( pX!=0 );
assert( pTerm->leftCursor==iCur );
sqlite3ExprCode(pParse, pX->pRight);
sqlite3VdbeAddOp(v, OP_ForceInt, pX->op==TK_LE || pX->op==TK_GT, brk);
sqlite3VdbeAddOp(v, bRev ? OP_MoveLt : OP_MoveGe, iCur, brk);
VdbeComment((v, "pk"));
disableTerm(pLevel, pTerm);
}else{
sqlite3VdbeAddOp(v, bRev ? OP_Last : OP_Rewind, iCur, brk);
}
if( iDirectLt[i]>=0 ){
Expr *pX;
k = iDirectLt[i];
assert( k<wc.nTerm );
pTerm = &wc.a[k];
pX = pTerm->pExpr;
assert( pX!=0 );
assert( pTerm->leftCursor==iCur );
sqlite3ExprCode(pParse, pX->pRight);
pLevel->iMem = pParse->nMem++;
sqlite3VdbeAddOp(v, OP_MemStore, pLevel->iMem, 1);
if( pX->op==TK_LT || pX->op==TK_GT ){
testOp = bRev ? OP_Le : OP_Ge;
}else{
testOp = bRev ? OP_Lt : OP_Gt;
}
disableTerm(pLevel, pTerm);
}
start = sqlite3VdbeCurrentAddr(v);
pLevel->op = bRev ? OP_Prev : OP_Next;
pLevel->p1 = iCur;
pLevel->p2 = start;
if( testOp!=OP_Noop ){
sqlite3VdbeAddOp(v, OP_Rowid, iCur, 0);
sqlite3VdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
sqlite3VdbeAddOp(v, testOp, 'n', brk);
}
}else if( pIdx==0 ){
/* Case 4: There is no usable index. We must do a complete
** scan of the entire database table.
*/
int start;
int opRewind;
assert( omitTable==0 );
brk = pLevel->brk = sqlite3VdbeMakeLabel(v);
cont = pLevel->cont = sqlite3VdbeMakeLabel(v);
if( pLevel->bRev ){
opRewind = OP_Last;
pLevel->op = OP_Prev;
}else{
opRewind = OP_Rewind;
pLevel->op = OP_Next;
}
sqlite3VdbeAddOp(v, opRewind, iCur, brk);
start = sqlite3VdbeCurrentAddr(v);
pLevel->p1 = iCur;
pLevel->p2 = start;
}else{
/* Case 5: The WHERE clause term that refers to the right-most
** column of the index is an inequality. For example, if
** the index is on (x,y,z) and the WHERE clause is of the
** form "x=5 AND y<10" then this case is used. Only the
** right-most column can be an inequality - the rest must
** use the "==" operator.
**
** This case is also used when there are no WHERE clause
** constraints but an index is selected anyway, in order
** to force the output order to conform to an ORDER BY.
*/
int score = pLevel->score;
int nEqColumn = score/32;
int start;
int leFlag=0, geFlag=0;
int testOp;
/* Evaluate the equality constraints
*/
for(j=0; j<nEqColumn; j++){
pTerm = findTerm(&wc, iCur, pIdx->aiColumn[j], loopMask, TK_EQ, TK_EQ);
assert( pTerm!=0 );
assert( (pTerm->flags & TERM_CODED)==0 );
sqlite3ExprCode(pParse, pTerm->pExpr->pRight);
disableTerm(pLevel, pTerm);
}
/* Duplicate the equality term values because they will all be
** used twice: once to make the termination key and once to make the
** start key.
*/
for(j=0; j<nEqColumn; j++){
sqlite3VdbeAddOp(v, OP_Dup, nEqColumn-1, 0);
}
/* Labels for the beginning and end of the loop
*/
cont = pLevel->cont = sqlite3VdbeMakeLabel(v);
brk = pLevel->brk = sqlite3VdbeMakeLabel(v);
/* Generate the termination key. This is the key value that
** will end the search. There is no termination key if there
** are no equality terms and no "X<..." term.
**
** 2002-Dec-04: On a reverse-order scan, the so-called "termination"
** key computed here really ends up being the start key.
*/
if( (score & 4)!=0 ){
Expr *pX;
pTerm = findTerm(&wc, iCur, pIdx->aiColumn[j], loopMask, TK_LT, TK_LE);
assert( pTerm!=0 );
pX = pTerm->pExpr;
assert( (pTerm->flags & TERM_CODED)==0 );
sqlite3ExprCode(pParse, pX->pRight);
leFlag = pX->op==TK_LE;
disableTerm(pLevel, pTerm);
testOp = OP_IdxGE;
}else{
testOp = nEqColumn>0 ? OP_IdxGE : OP_Noop;
leFlag = 1;
}
if( testOp!=OP_Noop ){
int nCol = nEqColumn + ((score & 4)!=0);
pLevel->iMem = pParse->nMem++;
buildIndexProbe(v, nCol, brk, pIdx);
if( pLevel->bRev ){
int op = leFlag ? OP_MoveLe : OP_MoveLt;
sqlite3VdbeAddOp(v, op, iIdxCur, brk);
}else{
sqlite3VdbeAddOp(v, OP_MemStore, pLevel->iMem, 1);
}
}else if( pLevel->bRev ){
sqlite3VdbeAddOp(v, OP_Last, iIdxCur, brk);
}
/* Generate the start key. This is the key that defines the lower
** bound on the search. There is no start key if there are no
** equality terms and if there is no "X>..." term. In
** that case, generate a "Rewind" instruction in place of the
** start key search.
**
** 2002-Dec-04: In the case of a reverse-order search, the so-called
** "start" key really ends up being used as the termination key.
*/
if( (score & 8)!=0 ){
Expr *pX;
pTerm = findTerm(&wc, iCur, pIdx->aiColumn[j], loopMask, TK_GT, TK_GE);
assert( pTerm!=0 );
pX = pTerm->pExpr;
assert( (pTerm->flags & TERM_CODED)==0 );
sqlite3ExprCode(pParse, pX->pRight);
geFlag = pX->op==TK_GE;
disableTerm(pLevel, pTerm);
}else{
geFlag = 1;
}
if( nEqColumn>0 || (score&8)!=0 ){
int nCol = nEqColumn + ((score&8)!=0);
buildIndexProbe(v, nCol, brk, pIdx);
if( pLevel->bRev ){
pLevel->iMem = pParse->nMem++;
sqlite3VdbeAddOp(v, OP_MemStore, pLevel->iMem, 1);
testOp = OP_IdxLT;
}else{
int op = geFlag ? OP_MoveGe : OP_MoveGt;
sqlite3VdbeAddOp(v, op, iIdxCur, brk);
}
}else if( pLevel->bRev ){
testOp = OP_Noop;
}else{
sqlite3VdbeAddOp(v, OP_Rewind, iIdxCur, brk);
}
/* Generate the the top of the loop. If there is a termination
** key we have to test for that key and abort at the top of the
** loop.
*/
start = sqlite3VdbeCurrentAddr(v);
if( testOp!=OP_Noop ){
sqlite3VdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
sqlite3VdbeAddOp(v, testOp, iIdxCur, brk);
if( (leFlag && !pLevel->bRev) || (!geFlag && pLevel->bRev) ){
sqlite3VdbeChangeP3(v, -1, "+", P3_STATIC);
}
}
sqlite3VdbeAddOp(v, OP_RowKey, iIdxCur, 0);
sqlite3VdbeAddOp(v, OP_IdxIsNull, nEqColumn + ((score&4)!=0), cont);
if( !omitTable ){
sqlite3VdbeAddOp(v, OP_IdxRowid, iIdxCur, 0);
sqlite3VdbeAddOp(v, OP_MoveGe, iCur, 0);
}
/* Record the instruction used to terminate the loop.
*/
pLevel->op = pLevel->bRev ? OP_Prev : OP_Next;
pLevel->p1 = iIdxCur;
pLevel->p2 = start;
}
loopMask &= ~getMask(&maskSet, iCur);
/* Insert code to test every subexpression that can be completely
** computed using the current set of tables.
*/
for(pTerm=wc.a, j=wc.nTerm; j>0; j--, pTerm++){
Expr *pE;
if( pTerm->flags & (TERM_VIRTUAL|TERM_CODED) ) continue;
if( (pTerm->prereqAll & loopMask)!=0 ) continue;
pE = pTerm->pExpr;
assert( pE!=0 );
if( pLevel->iLeftJoin && !ExprHasProperty(pE, EP_FromJoin) ){
continue;
}
sqlite3ExprIfFalse(pParse, pE, cont, 1);
pTerm->flags |= TERM_CODED;
}
brk = cont;
/* For a LEFT OUTER JOIN, generate code that will record the fact that
** at least one row of the right table has matched the left table.
*/
if( pLevel->iLeftJoin ){
pLevel->top = sqlite3VdbeCurrentAddr(v);
sqlite3VdbeAddOp(v, OP_Integer, 1, 0);
sqlite3VdbeAddOp(v, OP_MemStore, pLevel->iLeftJoin, 1);
VdbeComment((v, "# record LEFT JOIN hit"));
for(pTerm=wc.a, j=0; j<wc.nTerm; j++, pTerm++){
if( pTerm->flags & (TERM_VIRTUAL|TERM_CODED) ) continue;
if( (pTerm->prereqAll & loopMask)!=0 ) continue;
assert( pTerm->pExpr );
sqlite3ExprIfFalse(pParse, pTerm->pExpr, cont, 1);
pTerm->flags |= TERM_CODED;
}
}
}
pWInfo->iContinue = cont;
freeMaskSet(&maskSet);
whereClauseClear(&wc);
return pWInfo;
}
/*
** Generate the end of the WHERE loop. See comments on
** sqlite3WhereBegin() for additional information.
*/
void sqlite3WhereEnd(WhereInfo *pWInfo){
Vdbe *v = pWInfo->pParse->pVdbe;
int i;
WhereLevel *pLevel;
SrcList *pTabList = pWInfo->pTabList;
struct SrcList_item *pTabItem;
/* Generate loop termination code.
*/
for(i=pTabList->nSrc-1; i>=0; i--){
pLevel = &pWInfo->a[i];
sqlite3VdbeResolveLabel(v, pLevel->cont);
if( pLevel->op!=OP_Noop ){
sqlite3VdbeAddOp(v, pLevel->op, pLevel->p1, pLevel->p2);
}
sqlite3VdbeResolveLabel(v, pLevel->brk);
if( pLevel->inOp!=OP_Noop ){
sqlite3VdbeAddOp(v, pLevel->inOp, pLevel->inP1, pLevel->inP2);
}
if( pLevel->iLeftJoin ){
int addr;
addr = sqlite3VdbeAddOp(v, OP_MemLoad, pLevel->iLeftJoin, 0);
sqlite3VdbeAddOp(v, OP_NotNull, 1, addr+4 + (pLevel->iIdxCur>=0));
sqlite3VdbeAddOp(v, OP_NullRow, pTabList->a[i].iCursor, 0);
if( pLevel->iIdxCur>=0 ){
sqlite3VdbeAddOp(v, OP_NullRow, pLevel->iIdxCur, 0);
}
sqlite3VdbeAddOp(v, OP_Goto, 0, pLevel->top);
}
}
/* The "break" point is here, just past the end of the outer loop.
** Set it.
*/
sqlite3VdbeResolveLabel(v, pWInfo->iBreak);
/* Close all of the cursors that were opend by sqlite3WhereBegin.
*/
pLevel = pWInfo->a;
pTabItem = pTabList->a;
for(i=0; i<pTabList->nSrc; i++, pTabItem++, pLevel++){
Table *pTab = pTabItem->pTab;
assert( pTab!=0 );
if( pTab->isTransient || pTab->pSelect ) continue;
if( (pLevel->score & 1)==0 ){
sqlite3VdbeAddOp(v, OP_Close, pTabItem->iCursor, 0);
}
if( pLevel->pIdx!=0 ){
sqlite3VdbeAddOp(v, OP_Close, pLevel->iIdxCur, 0);
}
/* Make cursor substitutions for cases where we want to use
** just the index and never reference the table.
**
** Calls to the code generator in between sqlite3WhereBegin and
** sqlite3WhereEnd will have created code that references the table
** directly. This loop scans all that code looking for opcodes
** that reference the table and converts them into opcodes that
** reference the index.
*/
if( pLevel->score & 1 ){
int i, j, last;
VdbeOp *pOp;
Index *pIdx = pLevel->pIdx;
assert( pIdx!=0 );
pOp = sqlite3VdbeGetOp(v, pWInfo->iTop);
last = sqlite3VdbeCurrentAddr(v);
for(i=pWInfo->iTop; i<last; i++, pOp++){
if( pOp->p1!=pLevel->iTabCur ) continue;
if( pOp->opcode==OP_Column ){
pOp->p1 = pLevel->iIdxCur;
for(j=0; j<pIdx->nColumn; j++){
if( pOp->p2==pIdx->aiColumn[j] ){
pOp->p2 = j;
break;
}
}
}else if( pOp->opcode==OP_Rowid ){
pOp->p1 = pLevel->iIdxCur;
pOp->opcode = OP_IdxRowid;
}else if( pOp->opcode==OP_NullRow ){
pOp->opcode = OP_Noop;
}
}
}
}
/* Final cleanup
*/
sqliteFree(pWInfo);
return;
}
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