/*-------------------------------------------------------------------------
*
* parse_collate.c
* Routines for assigning collation information.
*
* We choose to handle collation analysis in a post-pass over the output
* of expression parse analysis. This is because we need more state to
* perform this processing than is needed in the finished tree. If we
* did it on-the-fly while building the tree, all that state would have
* to be kept in expression node trees permanently. This way, the extra
* storage is just local variables in this recursive routine.
*
* The info that is actually saved in the finished tree is:
* 1. The output collation of each expression node, or InvalidOid if it
* returns a noncollatable data type. This can also be InvalidOid if the
* result type is collatable but the collation is indeterminate.
* 2. The collation to be used in executing each function. InvalidOid means
* that there are no collatable inputs or their collation is indeterminate.
* This value is only stored in node types that might call collation-using
* functions.
*
* You might think we could get away with storing only one collation per
* node, but the two concepts really need to be kept distinct. Otherwise
* it's too confusing when a function produces a collatable output type but
* has no collatable inputs or produces noncollatable output from collatable
* inputs.
*
* Cases with indeterminate collation might result in an error being thrown
* at runtime. If we knew exactly which functions require collation
* information, we could throw those errors at parse time instead.
*
* Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/parser/parse_collate.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "catalog/pg_aggregate.h"
#include "catalog/pg_collation.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "parser/parse_collate.h"
#include "utils/lsyscache.h"
/*
* Collation strength (the SQL standard calls this "derivation"). Order is
* chosen to allow comparisons to work usefully. Note: the standard doesn't
* seem to distinguish between NONE and CONFLICT.
*/
typedef enum
{
COLLATE_NONE, /* expression is of a noncollatable datatype */
COLLATE_IMPLICIT, /* collation was derived implicitly */
COLLATE_CONFLICT, /* we had a conflict of implicit collations */
COLLATE_EXPLICIT /* collation was derived explicitly */
} CollateStrength;
typedef struct
{
ParseState *pstate; /* parse state (for error reporting) */
Oid collation; /* OID of current collation, if any */
CollateStrength strength; /* strength of current collation choice */
int location; /* location of expr that set collation */
/* Remaining fields are only valid when strength == COLLATE_CONFLICT */
Oid collation2; /* OID of conflicting collation */
int location2; /* location of expr that set collation2 */
} assign_collations_context;
static bool assign_query_collations_walker(Node *node, ParseState *pstate);
static bool assign_collations_walker(Node *node,
assign_collations_context *context);
static void merge_collation_state(Oid collation,
CollateStrength strength,
int location,
Oid collation2,
int location2,
assign_collations_context *context);
static void assign_aggregate_collations(Aggref *aggref,
assign_collations_context *loccontext);
static void assign_ordered_set_collations(Aggref *aggref,
assign_collations_context *loccontext);
static void assign_hypothetical_collations(Aggref *aggref,
assign_collations_context *loccontext);
/*
* assign_query_collations()
* Mark all expressions in the given Query with collation information.
*
* This should be applied to each Query after completion of parse analysis
* for expressions. Note that we do not recurse into sub-Queries, since
* those should have been processed when built.
*/
void
assign_query_collations(ParseState *pstate, Query *query)
{
/*
* We just use query_tree_walker() to visit all the contained expressions.
* We can skip the rangetable and CTE subqueries, though, since RTEs and
* subqueries had better have been processed already (else Vars referring
* to them would not get created with the right collation).
*/
(void) query_tree_walker(query,
assign_query_collations_walker,
(void *) pstate,
QTW_IGNORE_RANGE_TABLE |
QTW_IGNORE_CTE_SUBQUERIES);
}
/*
* Walker for assign_query_collations
*
* Each expression found by query_tree_walker is processed independently.
* Note that query_tree_walker may pass us a whole List, such as the
* targetlist, in which case each subexpression must be processed
* independently --- we don't want to bleat if two different targetentries
* have different collations.
*/
static bool
assign_query_collations_walker(Node *node, ParseState *pstate)
{
/* Need do nothing for empty subexpressions */
if (node == NULL)
return false;
/*
* We don't want to recurse into a set-operations tree; it's already been
* fully processed in transformSetOperationStmt.
*/
if (IsA(node, SetOperationStmt))
return false;
if (IsA(node, List))
assign_list_collations(pstate, (List *) node);
else
assign_expr_collations(pstate, node);
return false;
}
/*
* assign_list_collations()
* Mark all nodes in the list of expressions with collation information.
*
* The list member expressions are processed independently; they do not have
* to share a common collation.
*/
void
assign_list_collations(ParseState *pstate, List *exprs)
{
ListCell *lc;
foreach(lc, exprs)
{
Node *node = (Node *) lfirst(lc);
assign_expr_collations(pstate, node);
}
}
/*
* assign_expr_collations()
* Mark all nodes in the given expression tree with collation information.
*
* This is exported for the benefit of various utility commands that process
* expressions without building a complete Query. It should be applied after
* calling transformExpr() plus any expression-modifying operations such as
* coerce_to_boolean().
*/
void
assign_expr_collations(ParseState *pstate, Node *expr)
{
assign_collations_context context;
/* initialize context for tree walk */
context.pstate = pstate;
context.collation = InvalidOid;
context.strength = COLLATE_NONE;
context.location = -1;
/* and away we go */
(void) assign_collations_walker(expr, &context);
}
/*
* select_common_collation()
* Identify a common collation for a list of expressions.
*
* The expressions should all return the same datatype, else this is not
* terribly meaningful.
*
* none_ok means that it is permitted to return InvalidOid, indicating that
* no common collation could be identified, even for collatable datatypes.
* Otherwise, an error is thrown for conflict of implicit collations.
*
* In theory, none_ok = true reflects the rules of SQL standard clause "Result
* of data type combinations", none_ok = false reflects the rules of clause
* "Collation determination" (in some cases invoked via "Grouping
* operations").
*/
Oid
select_common_collation(ParseState *pstate, List *exprs, bool none_ok)
{
assign_collations_context context;
/* initialize context for tree walk */
context.pstate = pstate;
context.collation = InvalidOid;
context.strength = COLLATE_NONE;
context.location = -1;
/* and away we go */
(void) assign_collations_walker((Node *) exprs, &context);
/* deal with collation conflict */
if (context.strength == COLLATE_CONFLICT)
{
if (none_ok)
return InvalidOid;
ereport(ERROR,
(errcode(ERRCODE_COLLATION_MISMATCH),
errmsg("collation mismatch between implicit collations \"%s\" and \"%s\"",
get_collation_name(context.collation),
get_collation_name(context.collation2)),
errhint("You can choose the collation by applying the COLLATE clause to one or both expressions."),
parser_errposition(context.pstate, context.location2)));
}
/*
* Note: if strength is still COLLATE_NONE, we'll return InvalidOid, but
* that's okay because it must mean none of the expressions returned
* collatable datatypes.
*/
return context.collation;
}
/*
* assign_collations_walker()
* Recursive guts of collation processing.
*
* Nodes with no children (eg, Vars, Consts, Params) must have been marked
* when built. All upper-level nodes are marked here.
*
* Note: if this is invoked directly on a List, it will attempt to infer a
* common collation for all the list members. In particular, it will throw
* error if there are conflicting explicit collations for different members.
*/
static bool
assign_collations_walker(Node *node, assign_collations_context *context)
{
assign_collations_context loccontext;
Oid collation;
CollateStrength strength;
int location;
/* Need do nothing for empty subexpressions */
if (node == NULL)
return false;
/*
* Prepare for recursion. For most node types, though not all, the first
* thing we do is recurse to process all nodes below this one. Each level
* of the tree has its own local context.
*/
loccontext.pstate = context->pstate;
loccontext.collation = InvalidOid;
loccontext.strength = COLLATE_NONE;
loccontext.location = -1;
/* Set these fields just to suppress uninitialized-value warnings: */
loccontext.collation2 = InvalidOid;
loccontext.location2 = -1;
/*
* Recurse if appropriate, then determine the collation for this node.
*
* Note: the general cases are at the bottom of the switch, after various
* special cases.
*/
switch (nodeTag(node))
{
case T_CollateExpr:
{
/*
* COLLATE sets an explicitly derived collation, regardless of
* what the child state is. But we must recurse to set up
* collation info below here.
*/
CollateExpr *expr = (CollateExpr *) node;
(void) expression_tree_walker(node,
assign_collations_walker,
(void *) &loccontext);
collation = expr->collOid;
Assert(OidIsValid(collation));
strength = COLLATE_EXPLICIT;
location = expr->location;
}
break;
case T_FieldSelect:
{
/*
* For FieldSelect, the result has the field's declared
* collation, independently of what happened in the arguments.
* (The immediate argument must be composite and thus not
* collatable, anyhow.) The field's collation was already
* looked up and saved in the node.
*/
FieldSelect *expr = (FieldSelect *) node;
/* ... but first, recurse */
(void) expression_tree_walker(node,
assign_collations_walker,
(void *) &loccontext);
if (OidIsValid(expr->resultcollid))
{
/* Node's result type is collatable. */
/* Pass up field's collation as an implicit choice. */
collation = expr->resultcollid;
strength = COLLATE_IMPLICIT;
location = exprLocation(node);
}
else
{
/* Node's result type isn't collatable. */
collation = InvalidOid;
strength = COLLATE_NONE;
location = -1; /* won't be used */
}
}
break;
case T_RowExpr:
{
/*
* RowExpr is a special case because the subexpressions are
* independent: we don't want to complain if some of them have
* incompatible explicit collations.
*/
RowExpr *expr = (RowExpr *) node;
assign_list_collations(context->pstate, expr->args);
/*
* Since the result is always composite and therefore never
* has a collation, we can just stop here: this node has no
* impact on the collation of its parent.
*/
return false; /* done */
}
case T_RowCompareExpr:
{
/*
* For RowCompare, we have to find the common collation of
* each pair of input columns and build a list. If we can't
* find a common collation, we just put InvalidOid into the
* list, which may or may not cause an error at runtime.
*/
RowCompareExpr *expr = (RowCompareExpr *) node;
List *colls = NIL;
ListCell *l;
ListCell *r;
forboth(l, expr->largs, r, expr->rargs)
{
Node *le = (Node *) lfirst(l);
Node *re = (Node *) lfirst(r);
Oid coll;
coll = select_common_collation(context->pstate,
list_make2(le, re),
true);
colls = lappend_oid(colls, coll);
}
expr->inputcollids = colls;
/*
* Since the result is always boolean and therefore never has
* a collation, we can just stop here: this node has no impact
* on the collation of its parent.
*/
return false; /* done */
}
case T_CoerceToDomain:
{
/*
* If the domain declaration included a non-default COLLATE
* spec, then use that collation as the output collation of
* the coercion. Otherwise allow the input collation to
* bubble up. (The input should be of the domain's base type,
* therefore we don't need to worry about it not being
* collatable when the domain is.)
*/
CoerceToDomain *expr = (CoerceToDomain *) node;
Oid typcollation = get_typcollation(expr->resulttype);
/* ... but first, recurse */
(void) expression_tree_walker(node,
assign_collations_walker,
(void *) &loccontext);
if (OidIsValid(typcollation))
{
/* Node's result type is collatable. */
if (typcollation == DEFAULT_COLLATION_OID)
{
/* Collation state bubbles up from child. */
collation = loccontext.collation;
strength = loccontext.strength;
location = loccontext.location;
}
else
{
/* Use domain's collation as an implicit choice. */
collation = typcollation;
strength = COLLATE_IMPLICIT;
location = exprLocation(node);
}
}
else
{
/* Node's result type isn't collatable. */
collation = InvalidOid;
strength = COLLATE_NONE;
location = -1; /* won't be used */
}
/*
* Save the state into the expression node. We know it
* doesn't care about input collation.
*/
if (strength == COLLATE_CONFLICT)
exprSetCollation(node, InvalidOid);
else
exprSetCollation(node, collation);
}
break;
case T_TargetEntry:
(void) expression_tree_walker(node,
assign_collations_walker,
(void *) &loccontext);
/*
* TargetEntry can have only one child, and should bubble that
* state up to its parent. We can't use the general-case code
* below because exprType and friends don't work on TargetEntry.
*/
collation = loccontext.collation;
strength = loccontext.strength;
location = loccontext.location;
/*
* Throw error if the collation is indeterminate for a TargetEntry
* that is a sort/group target. We prefer to do this now, instead
* of leaving the comparison functions to fail at runtime, because
* we can give a syntax error pointer to help locate the problem.
* There are some cases where there might not be a failure, for
* example if the planner chooses to use hash aggregation instead
* of sorting for grouping; but it seems better to predictably
* throw an error. (Compare transformSetOperationTree, which will
* throw error for indeterminate collation of set-op columns, even
* though the planner might be able to implement the set-op
* without sorting.)
*/
if (strength == COLLATE_CONFLICT &&
((TargetEntry *) node)->ressortgroupref != 0)
ereport(ERROR,
(errcode(ERRCODE_COLLATION_MISMATCH),
errmsg("collation mismatch between implicit collations \"%s\" and \"%s\"",
get_collation_name(loccontext.collation),
get_collation_name(loccontext.collation2)),
errhint("You can choose the collation by applying the COLLATE clause to one or both expressions."),
parser_errposition(context->pstate,
loccontext.location2)));
break;
case T_InferenceElem:
case T_RangeTblRef:
case T_JoinExpr:
case T_FromExpr:
case T_OnConflictExpr:
case T_SortGroupClause:
(void) expression_tree_walker(node,
assign_collations_walker,
(void *) &loccontext);
/*
* When we're invoked on a query's jointree, we don't need to do
* anything with join nodes except recurse through them to process
* WHERE/ON expressions. So just stop here. Likewise, we don't
* need to do anything when invoked on sort/group lists.
*/
return false;
case T_Query:
{
/*
* We get here when we're invoked on the Query belonging to a
* SubLink. Act as though the Query returns its first output
* column, which indeed is what it does for EXPR_SUBLINK and
* ARRAY_SUBLINK cases. In the cases where the SubLink
* returns boolean, this info will be ignored. Special case:
* in EXISTS, the Query might return no columns, in which case
* we need do nothing.
*
* We needn't recurse, since the Query is already processed.
*/
Query *qtree = (Query *) node;
TargetEntry *tent;
if (qtree->targetList == NIL)
return false;
tent = linitial_node(TargetEntry, qtree->targetList);
if (tent->resjunk)
return false;
collation = exprCollation((Node *) tent->expr);
/* collation doesn't change if it's converted to array */
strength = COLLATE_IMPLICIT;
location = exprLocation((Node *) tent->expr);
}
break;
case T_List:
(void) expression_tree_walker(node,
assign_collations_walker,
(void *) &loccontext);
/*
* When processing a list, collation state just bubbles up from
* the list elements.
*/
collation = loccontext.collation;
strength = loccontext.strength;
location = loccontext.location;
break;
case T_Var:
case T_Const:
case T_Param:
case T_CoerceToDomainValue:
case T_CaseTestExpr:
case T_SetToDefault:
case T_CurrentOfExpr:
/*
* General case for childless expression nodes. These should
* already have a collation assigned; it is not this function's
* responsibility to look into the catalogs for base-case
* information.
*/
collation = exprCollation(node);
/*
* Note: in most cases, there will be an assigned collation
* whenever type_is_collatable(exprType(node)); but an exception
* occurs for a Var referencing a subquery output column for which
* a unique collation was not determinable. That may lead to a
* runtime failure if a collation-sensitive function is applied to
* the Var.
*/
if (OidIsValid(collation))
strength = COLLATE_IMPLICIT;
else
strength = COLLATE_NONE;
location = exprLocation(node);
break;
default:
{
/*
* General case for most expression nodes with children. First
* recurse, then figure out what to assign to this node.
*/
Oid typcollation;
/*
* For most node types, we want to treat all the child
* expressions alike; but there are a few exceptions, hence
* this inner switch.
*/
switch (nodeTag(node))
{
case T_Aggref:
{
/*
* Aggref is messy enough that we give it its own
* function, in fact three of them. The FILTER
* clause is independent of the rest of the
* aggregate, however, so it can be processed
* separately.
*/
Aggref *aggref = (Aggref *) node;
switch (aggref->aggkind)
{
case AGGKIND_NORMAL:
assign_aggregate_collations(aggref,
&loccontext);
break;
case AGGKIND_ORDERED_SET:
assign_ordered_set_collations(aggref,
&loccontext);
break;
case AGGKIND_HYPOTHETICAL:
assign_hypothetical_collations(aggref,
&loccontext);
break;
default:
elog(ERROR, "unrecognized aggkind: %d",
(int) aggref->aggkind);
}
assign_expr_collations(context->pstate,
(Node *) aggref->aggfilter);
}
break;
case T_WindowFunc:
{
/*
* WindowFunc requires special processing only for
* its aggfilter clause, as for aggregates.
*/
WindowFunc *wfunc = (WindowFunc *) node;
(void) assign_collations_walker((Node *) wfunc->args,
&loccontext);
assign_expr_collations(context->pstate,
(Node *) wfunc->aggfilter);
}
break;
case T_CaseExpr:
{
/*
* CaseExpr is a special case because we do not
* want to recurse into the test expression (if
* any). It was already marked with collations
* during transformCaseExpr, and furthermore its
* collation is not relevant to the result of the
* CASE --- only the output expressions are.
*/
CaseExpr *expr = (CaseExpr *) node;
ListCell *lc;
foreach(lc, expr->args)
{
CaseWhen *when = lfirst_node(CaseWhen, lc);
/*
* The condition expressions mustn't affect
* the CASE's result collation either; but
* since they are known to yield boolean, it's
* safe to recurse directly on them --- they
* won't change loccontext.
*/
(void) assign_collations_walker((Node *) when->expr,
&loccontext);
(void) assign_collations_walker((Node *) when->result,
&loccontext);
}
(void) assign_collations_walker((Node *) expr->defresult,
&loccontext);
}
break;
default:
/*
* Normal case: all child expressions contribute
* equally to loccontext.
*/
(void) expression_tree_walker(node,
assign_collations_walker,
(void *) &loccontext);
break;
}
/*
* Now figure out what collation to assign to this node.
*/
typcollation = get_typcollation(exprType(node));
if (OidIsValid(typcollation))
{
/* Node's result is collatable; what about its input? */
if (loccontext.strength > COLLATE_NONE)
{
/* Collation state bubbles up from children. */
collation = loccontext.collation;
strength = loccontext.strength;
location = loccontext.location;
}
else
{
/*
* Collatable output produced without any collatable
* input. Use the type's collation (which is usually
* DEFAULT_COLLATION_OID, but might be different for a
* domain).
*/
collation = typcollation;
strength = COLLATE_IMPLICIT;
location = exprLocation(node);
}
}
else
{
/* Node's result type isn't collatable. */
collation = InvalidOid;
strength = COLLATE_NONE;
location = -1; /* won't be used */
}
/*
* Save the result collation into the expression node. If the
* state is COLLATE_CONFLICT, we'll set the collation to
* InvalidOid, which might result in an error at runtime.
*/
if (strength == COLLATE_CONFLICT)
exprSetCollation(node, InvalidOid);
else
exprSetCollation(node, collation);
/*
* Likewise save the input collation, which is the one that
* any function called by this node should use.
*/
if (loccontext.strength == COLLATE_CONFLICT)
exprSetInputCollation(node, InvalidOid);
else
exprSetInputCollation(node, loccontext.collation);
}
break;
}
/*
* Now, merge my information into my parent's state.
*/
merge_collation_state(collation,
strength,
location,
loccontext.collation2,
loccontext.location2,
context);
return false;
}
/*
* Merge collation state of a subexpression into the context for its parent.
*/
static void
merge_collation_state(Oid collation,
CollateStrength strength,
int location,
Oid collation2,
int location2,
assign_collations_context *context)
{
/*
* If the collation strength for this node is different from what's
* already in *context, then this node either dominates or is dominated by
* earlier siblings.
*/
if (strength > context->strength)
{
/* Override previous parent state */
context->collation = collation;
context->strength = strength;
context->location = location;
/* Bubble up error info if applicable */
if (strength == COLLATE_CONFLICT)
{
context->collation2 = collation2;
context->location2 = location2;
}
}
else if (strength == context->strength)
{
/* Merge, or detect error if there's a collation conflict */
switch (strength)
{
case COLLATE_NONE:
/* Nothing + nothing is still nothing */
break;
case COLLATE_IMPLICIT:
if (collation != context->collation)
{
/*
* Non-default implicit collation always beats default.
*/
if (context->collation == DEFAULT_COLLATION_OID)
{
/* Override previous parent state */
context->collation = collation;
context->strength = strength;
context->location = location;
}
else if (collation != DEFAULT_COLLATION_OID)
{
/*
* Oops, we have a conflict. We cannot throw error
* here, since the conflict could be resolved by a
* later sibling CollateExpr, or the parent might not
* care about collation anyway. Return enough info to
* throw the error later, if needed.
*/
context->strength = COLLATE_CONFLICT;
context->collation2 = collation;
context->location2 = location;
}
}
break;
case COLLATE_CONFLICT:
/* We're still conflicted ... */
break;
case COLLATE_EXPLICIT:
if (collation != context->collation)
{
/*
* Oops, we have a conflict of explicit COLLATE clauses.
* Here we choose to throw error immediately; that is what
* the SQL standard says to do, and there's no good reason
* to be less strict.
*/
ereport(ERROR,
(errcode(ERRCODE_COLLATION_MISMATCH),
errmsg("collation mismatch between explicit collations \"%s\" and \"%s\"",
get_collation_name(context->collation),
get_collation_name(collation)),
parser_errposition(context->pstate, location)));
}
break;
}
}
}
/*
* Aggref is a special case because expressions used only for ordering
* shouldn't be taken to conflict with each other or with regular args,
* indeed shouldn't affect the aggregate's result collation at all.
* We handle this by applying assign_expr_collations() to them rather than
* passing down our loccontext.
*
* Note that we recurse to each TargetEntry, not directly to its contained
* expression, so that the case above for T_TargetEntry will complain if we
* can't resolve a collation for an ORDER BY item (whether or not it is also
* a normal aggregate arg).
*
* We need not recurse into the aggorder or aggdistinct lists, because those
* contain only SortGroupClause nodes which we need not process.
*/
static void
assign_aggregate_collations(Aggref *aggref,
assign_collations_context *loccontext)
{
ListCell *lc;
/* Plain aggregates have no direct args */
Assert(aggref->aggdirectargs == NIL);
/* Process aggregated args, holding resjunk ones at arm's length */
foreach(lc, aggref->args)
{
TargetEntry *tle = lfirst_node(TargetEntry, lc);
if (tle->resjunk)
assign_expr_collations(loccontext->pstate, (Node *) tle);
else
(void) assign_collations_walker((Node *) tle, loccontext);
}
}
/*
* For ordered-set aggregates, it's somewhat unclear how best to proceed.
* The spec-defined inverse distribution functions have only one sort column
* and don't return collatable types, but this is clearly too restrictive in
* the general case. Our solution is to consider that the aggregate's direct
* arguments contribute normally to determination of the aggregate's own
* collation, while aggregated arguments contribute only when the aggregate
* is designed to have exactly one aggregated argument (i.e., it has a single
* aggregated argument and is non-variadic). If it can have more than one
* aggregated argument, we process the aggregated arguments as independent
* sort columns. This avoids throwing error for something like
* agg(...) within group (order by x collate "foo", y collate "bar")
* while also guaranteeing that variadic aggregates don't change in behavior
* depending on how many sort columns a particular call happens to have.
*
* Otherwise this is much like the plain-aggregate case.
*/
static void
assign_ordered_set_collations(Aggref *aggref,
assign_collations_context *loccontext)
{
bool merge_sort_collations;
ListCell *lc;
/* Merge sort collations to parent only if there can be only one */
merge_sort_collations = (list_length(aggref->args) == 1 &&
get_func_variadictype(aggref->aggfnoid) == InvalidOid);
/* Direct args, if any, are normal children of the Aggref node */
(void) assign_collations_walker((Node *) aggref->aggdirectargs,
loccontext);
/* Process aggregated args appropriately */
foreach(lc, aggref->args)
{
TargetEntry *tle = lfirst_node(TargetEntry, lc);
if (merge_sort_collations)
(void) assign_collations_walker((Node *) tle, loccontext);
else
assign_expr_collations(loccontext->pstate, (Node *) tle);
}
}
/*
* Hypothetical-set aggregates are even more special: per spec, we need to
* unify the collations of each pair of hypothetical and aggregated args.
* And we need to force the choice of collation down into the sort column
* to ensure that the sort happens with the chosen collation. Other than
* that, the behavior is like regular ordered-set aggregates. Note that
* hypothetical direct arguments contribute to the aggregate collation
* only when their partner aggregated arguments do.
*/
static void
assign_hypothetical_collations(Aggref *aggref,
assign_collations_context *loccontext)
{
ListCell *h_cell = list_head(aggref->aggdirectargs);
ListCell *s_cell = list_head(aggref->args);
bool merge_sort_collations;
int extra_args;
/* Merge sort collations to parent only if there can be only one */
merge_sort_collations = (list_length(aggref->args) == 1 &&
get_func_variadictype(aggref->aggfnoid) == InvalidOid);
/* Process any non-hypothetical direct args */
extra_args = list_length(aggref->aggdirectargs) - list_length(aggref->args);
Assert(extra_args >= 0);
while (extra_args-- > 0)
{
(void) assign_collations_walker((Node *) lfirst(h_cell), loccontext);
h_cell = lnext(h_cell);
}
/* Scan hypothetical args and aggregated args in parallel */
while (h_cell && s_cell)
{
Node *h_arg = (Node *) lfirst(h_cell);
TargetEntry *s_tle = (TargetEntry *) lfirst(s_cell);
assign_collations_context paircontext;
/*
* Assign collations internally in this pair of expressions, then
* choose a common collation for them. This should match
* select_common_collation(), but we can't use that function as-is
* because we need access to the whole collation state so we can
* bubble it up to the aggregate function's level.
*/
paircontext.pstate = loccontext->pstate;
paircontext.collation = InvalidOid;
paircontext.strength = COLLATE_NONE;
paircontext.location = -1;
/* Set these fields just to suppress uninitialized-value warnings: */
paircontext.collation2 = InvalidOid;
paircontext.location2 = -1;
(void) assign_collations_walker(h_arg, &paircontext);
(void) assign_collations_walker((Node *) s_tle->expr, &paircontext);
/* deal with collation conflict */
if (paircontext.strength == COLLATE_CONFLICT)
ereport(ERROR,
(errcode(ERRCODE_COLLATION_MISMATCH),
errmsg("collation mismatch between implicit collations \"%s\" and \"%s\"",
get_collation_name(paircontext.collation),
get_collation_name(paircontext.collation2)),
errhint("You can choose the collation by applying the COLLATE clause to one or both expressions."),
parser_errposition(paircontext.pstate,
paircontext.location2)));
/*
* At this point paircontext.collation can be InvalidOid only if the
* type is not collatable; no need to do anything in that case. If we
* do have to change the sort column's collation, do it by inserting a
* RelabelType node into the sort column TLE.
*
* XXX This is pretty grotty for a couple of reasons:
* assign_collations_walker isn't supposed to be changing the
* expression structure like this, and a parse-time change of
* collation ought to be signaled by a CollateExpr not a RelabelType
* (the use of RelabelType for collation marking is supposed to be a
* planner/executor thing only). But we have no better alternative.
* In particular, injecting a CollateExpr could result in the
* expression being interpreted differently after dump/reload, since
* we might be effectively promoting an implicit collation to
* explicit. This kluge is relying on ruleutils.c not printing a
* COLLATE clause for a RelabelType, and probably on some other
* fragile behaviors.
*/
if (OidIsValid(paircontext.collation) &&
paircontext.collation != exprCollation((Node *) s_tle->expr))
{
s_tle->expr = (Expr *)
makeRelabelType(s_tle->expr,
exprType((Node *) s_tle->expr),
exprTypmod((Node *) s_tle->expr),
paircontext.collation,
COERCE_IMPLICIT_CAST);
}
/*
* If appropriate, merge this column's collation state up to the
* aggregate function.
*/
if (merge_sort_collations)
merge_collation_state(paircontext.collation,
paircontext.strength,
paircontext.location,
paircontext.collation2,
paircontext.location2,
loccontext);
h_cell = lnext(h_cell);
s_cell = lnext(s_cell);
}
Assert(h_cell == NULL && s_cell == NULL);
}