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An initial attempt to optimize VIEWs that occur as the right operand of a

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LEFT JOIN.  This particular check-in does not work correctly because it does
not deal with the case of columns in the VIEW that return non-NULL even when
all columns in the table of the VIEW are NULL because of the LEFT JOIN.

FossilOrigin-Name: 1838a59c8a1c151bd6fc822b0ffef661803cf0e4704c917e74a04567b81740b9
This commit is contained in:
drh 2017-04-14 17:18:45 +00:00
parent b1ed717f18
commit 399c7e21e4
3 changed files with 41 additions and 33 deletions
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17
manifest
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@ -1,5 +1,5 @@
C Make\sUSE_FULLWARN=1\sthe\sdefault\sfor\sMSVC\sand\sfix\sharmless\scompiler\swarnings.
D 2017-04-14T14:50:34.600
C An\sinitial\sattempt\sto\soptimize\sVIEWs\sthat\soccur\sas\sthe\sright\soperand\sof\sa\nLEFT\sJOIN.\s\sThis\sparticular\scheck-in\sdoes\snot\swork\scorrectly\sbecause\sit\sdoes\nnot\sdeal\swith\sthe\scase\sof\scolumns\sin\sthe\sVIEW\sthat\sreturn\snon-NULL\seven\swhen\nall\scolumns\sin\sthe\stable\sof\sthe\sVIEW\sare\sNULL\sbecause\sof\sthe\sLEFT\sJOIN.
D 2017-04-14T17:18:45.647
F Makefile.in 1cc758ce3374a32425e4d130c2fe7b026b20de5b8843243de75f087c0a2661fb
F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
F Makefile.msc 6a8c838220f7c00820e1fc0ac1bccaaa8e5676067e1dbfa1bafa7a4ffecf8ae6
@ -401,7 +401,7 @@ F src/printf.c 8757834f1b54dae512fb25eb1acc8e94a0d15dd2290b58f2563f65973265adb2
F src/random.c 80f5d666f23feb3e6665a6ce04c7197212a88384
F src/resolve.c 3e518b962d932a997fae373366880fc028c75706
F src/rowset.c 7b7e7e479212e65b723bf40128c7b36dc5afdfac
F src/select.c 4588dcfb0fa430012247a209ba08e17904dd32ec7690e9cb6c85e0ef012b0518
F src/select.c 52b29bdeaa4cf317a981b6e8d0a15ec9c16372a738ede51c2a285c03fc69d036
F src/shell.c 70f4957b988572315e97c56941fdc81fd35907fee36b7b2e7be5ec4c7e9d065d
F src/sqlite.h.in 40233103e3e4e10f8a63523498d0259d232e42aba478e2d3fb914799185aced6
F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
@ -1571,7 +1571,10 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
P 5159cb8f2bcfb1f7114786ba23082d2b91a26e3a7ddfae75f8bd362792949d5e
R 3270eeed59983be191492d424a0b906b
U mistachkin
Z edc8ddb73a9c8e57e014e4878b2c6186
P 6bf673767b8e5cedef1acff795cbe524fab8db2525c06424db4e038934a33936
R 8dfa3ca7454fc6936bedb04ccf47ee12
T *branch * left-join-view
T *sym-left-join-view *
T -sym-trunk *
U drh
Z 5ef873863ca7134987a034a627c04882

2
manifest.uuid
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@ -1 +1 @@
6bf673767b8e5cedef1acff795cbe524fab8db2525c06424db4e038934a33936
1838a59c8a1c151bd6fc822b0ffef661803cf0e4704c917e74a04567b81740b9

55
src/select.c
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@ -3154,6 +3154,7 @@ static int multiSelectOrderBy(
typedef struct SubstContext {
Parse *pParse; /* The parsing context */
int iTable; /* Replace references to this table */
int iNewTable; /* New table number, or -1 */
ExprList *pEList; /* Replacement expressions */
} SubstContext;
@ -3179,6 +3180,9 @@ static Expr *substExpr(
Expr *pExpr /* Expr in which substitution occurs */
){
if( pExpr==0 ) return 0;
if( ExprHasProperty(pExpr, EP_FromJoin) && pExpr->iRightJoinTable==pSubst->iTable ){
pExpr->iRightJoinTable = pSubst->iNewTable;
}
if( pExpr->op==TK_COLUMN && pExpr->iTable==pSubst->iTable ){
if( pExpr->iColumn<0 ){
pExpr->op = TK_NULL;
@ -3285,7 +3289,13 @@ static void substSelect(
** due to ticket [2f7170d73bf9abf80] from 2015-02-09.)
**
** (3) The subquery is not the right operand of a left outer join
** (Originally ticket #306. Strengthened by ticket #3300)
** or (3b) the subquery is not a join and (3c) does not contain any
** result-set columns that could be non-NULL even if columns of the
** subquery table are NULL.
** to be more restrictive - disallowing subquery if it was the
** right operand of a left join. See tickets #306 and #3300. Relaxed
** to allow simple subqueries as the right operand of a left join
** on 2017-04-14.)
**
** (4) The subquery is not DISTINCT.
**
@ -3403,6 +3413,8 @@ static int flattenSubquery(
SrcList *pSubSrc; /* The FROM clause of the subquery */
ExprList *pList; /* The result set of the outer query */
int iParent; /* VDBE cursor number of the pSub result set temp table */
int iNewParent = -1;/* Replacement table for iParent */
int isLeftJoin = 0; /* True if pSub is the right side of a LEFT JOIN */
int i; /* Loop counter */
Expr *pWhere; /* The WHERE clause */
struct SrcList_item *pSubitem; /* The subquery */
@ -3429,7 +3441,7 @@ static int flattenSubquery(
return 0; /* Restriction (2b) */
}
}
pSubSrc = pSub->pSrc;
assert( pSubSrc );
/* Prior to version 3.1.2, when LIMIT and OFFSET had to be simple constants,
@ -3467,10 +3479,9 @@ static int flattenSubquery(
return 0; /* Restriction (23) */
}
/* OBSOLETE COMMENT 1:
** Restriction 3: If the subquery is a join, make sure the subquery is
** not used as the right operand of an outer join. Examples of why this
** is not allowed:
/*
** If the subquery is the right operand of a LEFT JOIN, then the
** subquery may not be a join itself. Example of why this is not allowed:
**
** t1 LEFT OUTER JOIN (t2 JOIN t3)
**
@ -3480,27 +3491,15 @@ static int flattenSubquery(
**
** which is not at all the same thing.
**
** OBSOLETE COMMENT 2:
** Restriction 12: If the subquery is the right operand of a left outer
** join, make sure the subquery has no WHERE clause.
** An examples of why this is not allowed:
**
** t1 LEFT OUTER JOIN (SELECT * FROM t2 WHERE t2.x>0)
**
** If we flatten the above, we would get
**
** (t1 LEFT OUTER JOIN t2) WHERE t2.x>0
**
** But the t2.x>0 test will always fail on a NULL row of t2, which
** effectively converts the OUTER JOIN into an INNER JOIN.
**
** THIS OVERRIDES OBSOLETE COMMENTS 1 AND 2 ABOVE:
** Ticket #3300 shows that flattening the right term of a LEFT JOIN
** is fraught with danger. Best to avoid the whole thing. If the
** subquery is the right term of a LEFT JOIN, then do not flatten.
** See also tickets #306 and #3300.
*/
if( (pSubitem->fg.jointype & JT_OUTER)!=0 ){
return 0;
isLeftJoin = 1;
if( pSubSrc->nSrc>1 ){
return 0; /* Restriction (3b) */
}
/* TBD: Deal with the case of result-set expressions that are non-NULL even
** when the RHS table of a LEFT JOIN is NULL. */
}
/* Restriction 17: If the sub-query is a compound SELECT, then it must
@ -3709,6 +3708,7 @@ static int flattenSubquery(
sqlite3IdListDelete(db, pSrc->a[i+iFrom].pUsing);
assert( pSrc->a[i+iFrom].fg.isTabFunc==0 );
pSrc->a[i+iFrom] = pSubSrc->a[i];
iNewParent = pSubSrc->a[i].iCursor;
memset(&pSubSrc->a[i], 0, sizeof(pSubSrc->a[i]));
}
pSrc->a[iFrom].fg.jointype = jointype;
@ -3754,6 +3754,9 @@ static int flattenSubquery(
pSub->pOrderBy = 0;
}
pWhere = sqlite3ExprDup(db, pSub->pWhere, 0);
if( isLeftJoin ){
setJoinExpr(pWhere, iNewParent);
}
if( subqueryIsAgg ){
assert( pParent->pHaving==0 );
pParent->pHaving = pParent->pWhere;
@ -3770,6 +3773,7 @@ static int flattenSubquery(
SubstContext x;
x.pParse = pParse;
x.iTable = iParent;
x.iNewTable = iNewParent;
x.pEList = pSub->pEList;
substSelect(&x, pParent, 0);
}
@ -3878,6 +3882,7 @@ static int pushDownWhereTerms(
pNew = sqlite3ExprDup(pParse->db, pWhere, 0);
x.pParse = pParse;
x.iTable = iCursor;
x.iNewTable = iCursor;
x.pEList = pSubq->pEList;
pNew = substExpr(&x, pNew);
pSubq->pWhere = sqlite3ExprAnd(pParse->db, pSubq->pWhere, pNew);