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postgres/src/backend/parser/parse_clause.c

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/*-------------------------------------------------------------------------
*
* parse_clause.c
* handle clauses in parser
*
* Portions Copyright (c) 1996-2000, PostgreSQL, Inc
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/parser/parse_clause.c,v 1.64 2000/06/09 01:44:18 momjian Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/heapam.h"
#include "optimizer/tlist.h"
#include "nodes/makefuncs.h"
#include "parser/parse.h"
#include "parser/parse_clause.h"
#include "parser/parse_coerce.h"
#include "parser/parse_expr.h"
#include "parser/parse_oper.h"
#include "parser/parse_relation.h"
#include "parser/parse_target.h"
#define ORDER_CLAUSE 0
#define GROUP_CLAUSE 1
#define DISTINCT_ON_CLAUSE 2
static char *clauseText[] = {"ORDER BY", "GROUP BY", "DISTINCT ON"};
static TargetEntry *findTargetlistEntry(ParseState *pstate, Node *node,
List *tlist, int clause);
static void parseFromClause(ParseState *pstate, List *frmList);
static RangeTblEntry *transformTableEntry(ParseState *pstate, RangeVar *r);
static List *addTargetToSortList(TargetEntry *tle, List *sortlist,
List *targetlist, char *opname);
static bool exprIsInSortList(Node *expr, List *sortList, List *targetList);
#ifndef DISABLE_OUTER_JOINS
static List *transformUsingClause(ParseState *pstate, List *using,
List *left, List *right);
#endif
/*
* makeRangeTable -
* Build the initial range table from the FROM clause.
*/
void
makeRangeTable(ParseState *pstate, List *frmList)
{
/* Currently, nothing to do except this: */
parseFromClause(pstate, frmList);
}
/*
* setTargetTable
* Add the target relation of INSERT or UPDATE to the range table,
* and make the special links to it in the ParseState.
*
* Note that the target is not marked as either inFromCl or inJoinSet.
* For INSERT, we don't want the target to be joined to; it's a
* destination of tuples, not a source. For UPDATE/DELETE, we do
* need to scan or join the target. This will happen without the
* inJoinSet flag because the planner's preprocess_targetlist()
* adds the destination's CTID attribute to the targetlist, and
* therefore the destination will be a referenced table even if
* there is no other use of any of its attributes. Tricky, eh?
*/
void
setTargetTable(ParseState *pstate, char *relname, bool inh)
{
RangeTblEntry *rte;
/* look for relname only at current nesting level... */
if (refnameRangeTablePosn(pstate, relname, NULL) == 0)
rte = addRangeTableEntry(pstate, relname,
makeAttr(relname, NULL),
inh, FALSE, FALSE);
else
rte = refnameRangeTableEntry(pstate, relname);
/* This could only happen for multi-action rules */
if (pstate->p_target_relation != NULL)
heap_close(pstate->p_target_relation, AccessShareLock);
pstate->p_target_rangetblentry = rte;
pstate->p_target_relation = heap_open(rte->relid, AccessShareLock);
/* will close relation later, see analyze.c */
}
static Node *
mergeInnerJoinQuals(ParseState *pstate, Node *clause)
{
List *jquals;
foreach(jquals, pstate->p_join_quals)
{
Node *jqual = (Node *) lfirst(jquals);
if (clause == NULL)
clause = jqual;
else
{
A_Expr *a = makeNode(A_Expr);
a->oper = AND;
a->opname = NULL;
a->lexpr = clause;
a->rexpr = jqual;
clause = (Node *) a;
}
}
/* Make sure that we don't add same quals twice... */
pstate->p_join_quals = NIL;
return clause;
} /* mergeInnerJoinQuals() */
/*
* transformWhereClause -
* transforms the qualification and make sure it is of type Boolean
*/
Node *
transformWhereClause(ParseState *pstate, Node *clause)
{
Node *qual;
if (pstate->p_join_quals != NIL)
clause = mergeInnerJoinQuals(pstate, clause);
if (clause == NULL)
return NULL;
pstate->p_in_where_clause = true;
qual = transformExpr(pstate, clause, EXPR_COLUMN_FIRST);
pstate->p_in_where_clause = false;
if (exprType(qual) != BOOLOID)
{
elog(ERROR, "WHERE clause must return type bool, not type %s",
typeidTypeName(exprType(qual)));
}
return qual;
}
#ifndef DISABLE_JOIN_SYNTAX
char *
AttrString(Attr *attr);
char *
AttrString(Attr *attr)
{
Value *val;
Assert(length(attr->attrs) == 1);
val = lfirst(attr->attrs);
Assert(IsA(val, String));
return strVal(val);
}
List *
ListTableAsAttrs(ParseState *pstate, char *table);
List *
ListTableAsAttrs(ParseState *pstate, char *table)
{
Attr *attr = expandTable(pstate, table, TRUE);
List *rlist = NIL;
List *col;
foreach(col, attr->attrs)
{
Attr *a = makeAttr(table, strVal((Value *) lfirst(col)));
rlist = lappend(rlist, a);
}
return rlist;
}
List *
makeUniqueAttrList(List *candidates, List *idents);
List *
makeUniqueAttrList(List *attrs, List *filter)
{
List *result = NULL;
List *candidate;
foreach(candidate, attrs)
{
List *fmember;
bool match = FALSE;
Attr *cattr = lfirst(candidate);
Assert(IsA(cattr, Attr));
Assert(length(cattr->attrs) == 1);
foreach(fmember, filter)
{
Attr *fattr = lfirst(fmember);
Assert(IsA(fattr, Attr));
Assert(length(fattr->attrs) == 1);
if (strcmp(strVal(lfirst(cattr->attrs)), strVal(lfirst(fattr->attrs))) == 0)
{
match = TRUE;
break;
}
}
if (!match)
result = lappend(result, cattr);
}
return result;
}
List *
makeAttrList(Attr *attr);
List *
makeAttrList(Attr *attr)
{
List *result = NULL;
char *name = attr->relname;
List *col;
foreach(col, attr->attrs)
{
Attr *newattr = makeAttr(name, strVal((Value *) lfirst(col)));
result = lappend(result, newattr);
}
return result;
}
#ifdef NOT_USED
/* ExpandAttrs()
* Take an existing attribute node and return a list of attribute nodes
* with one attribute name per node.
*/
List *
ExpandAttrs(Attr *attr)
{
List *col;
char *relname = attr->relname;
List *rlist = NULL;
Assert(attr != NULL);
if ((attr->attrs == NULL) || (length(attr->attrs) <= 1))
return lcons(attr, NIL);
foreach(col, attr->attrs)
{
Attr *attr = lfirst(col);
rlist = lappend(rlist, makeAttr(relname, AttrString(attr)));
}
return rlist;
}
#endif
/* transformUsingClause()
* Take an ON or USING clause from a join expression and expand if necessary.
* Result is an implicitly-ANDed list of untransformed qualification clauses.
*/
static List *
transformUsingClause(ParseState *pstate, List *usingList,
List *leftList, List *rightList)
{
List *result = NIL;
List *using;
foreach(using, usingList)
{
Attr *uattr = lfirst(using);
Attr *lattr = NULL,
*rattr = NULL;
List *col;
A_Expr *e;
/*
* find the first instances of this column in the shape list and
* the last table in the shape list...
*/
foreach(col, leftList)
{
Attr *attr = lfirst(col);
if (strcmp(AttrString(attr), AttrString(uattr)) == 0)
{
lattr = attr;
break;
}
}
foreach(col, rightList)
{
Attr *attr = lfirst(col);
if (strcmp(AttrString(attr), AttrString(uattr)) == 0)
{
rattr = attr;
break;
}
}
Assert((lattr != NULL) && (rattr != NULL));
e = makeNode(A_Expr);
e->oper = OP;
e->opname = "=";
e->lexpr = (Node *) lattr;
e->rexpr = (Node *) rattr;
result = lappend(result, e);
}
return result;
} /* transformUsingClause() */
#endif
static RangeTblEntry *
transformTableEntry(ParseState *pstate, RangeVar *r)
{
RelExpr *baserel = r->relExpr;
char *relname = baserel->relname;
#if 0
char *refname;
List *columns;
#endif
RangeTblEntry *rte;
#if 0
if (r->name != NULL)
refname = r->name->relname;
else
refname = NULL;
columns = ListTableAsAttrs(pstate, relname);
/* alias might be specified... */
if (r->name != NULL)
{
#ifndef DISABLE_JOIN_SYNTAX
if (length(columns) > 0)
{
if (length(r->name->attrs) > 0)
{
if (length(columns) != length(r->name->attrs))
elog(ERROR, "'%s' has %d columns but %d %s specified",
relname, length(columns), length(r->name->attrs),
((length(r->name->attrs) != 1) ? "aliases" : "alias"));
aliasList = nconc(aliasList, r->name->attrs);
}
else
{
r->name->attrs = columns;
aliasList = nconc(aliasList, r->name->attrs);
}
}
else
elog(NOTICE, "transformTableEntry: column aliases not handled (internal error)");
#else
elog(ERROR, "Column aliases not yet supported");
#endif
}
else
{
refname = relname;
aliasList = nconc(aliasList, columns);
}
#endif
if (r->name == NULL)
r->name = makeAttr(relname, NULL);
/*
* marks this entry to indicate it comes from the FROM clause. In SQL,
* the target list can only refer to range variables specified in the
* from clause but we follow the more powerful POSTQUEL semantics and
* automatically generate the range variable if not specified. However
* there are times we need to know whether the entries are legitimate.
*
* eg. select * from foo f where f.x = 1; will generate wrong answer if
* we expand * to foo.x.
*/
rte = addRangeTableEntry(pstate, relname, r->name,
baserel->inh, TRUE, TRUE);
return rte;
} /* transformTableEntry() */
/*
* parseFromClause -
* turns the table references specified in the from-clause into a
* range table. The range table may grow as we transform the expressions
* in the target list. (Note that this happens because in POSTQUEL, we
* allow references to relations not specified in the from-clause. We
* also allow now as an extension.)
*
* The FROM clause can now contain JoinExpr nodes, which contain parsing info
* for inner and outer joins. The USING clause must be expanded into a qualification
* for an inner join at least, since that is compatible with the old syntax.
* Not sure yet how to handle outer joins, but it will become clear eventually?
* - thomas 1998-12-16
*/
static void
parseFromClause(ParseState *pstate, List *frmList)
{
List *fl;
foreach(fl, frmList)
{
Node *n = lfirst(fl);
/*
* marks this entry to indicate it comes from the FROM clause. In
* SQL, the target list can only refer to range variables
* specified in the from clause but we follow the more powerful
* POSTQUEL semantics and automatically generate the range
* variable if not specified. However there are times we need to
* know whether the entries are legitimate.
*
* eg. select * from foo f where f.x = 1; will generate wrong answer
* if we expand * to foo.x.
*/
/* Plain vanilla inner join, just like we've always had? */
if (IsA(n, RangeVar))
transformTableEntry(pstate, (RangeVar *) n);
/* A newfangled join expression? */
else if (IsA(n, JoinExpr))
{
#ifndef DISABLE_JOIN_SYNTAX
RangeTblEntry *l_rte,
*r_rte;
Attr *l_name,
*r_name = NULL;
JoinExpr *j = (JoinExpr *) n;
if (j->alias != NULL)
elog(ERROR, "JOIN table aliases are not supported");
/* nested join? then handle the left one first... */
if (IsA(j->larg, JoinExpr))
{
parseFromClause(pstate, lcons(j->larg, NIL));
l_name = ((JoinExpr *) j->larg)->alias;
}
else
{
Assert(IsA(j->larg, RangeVar));
l_rte = transformTableEntry(pstate, (RangeVar *) j->larg);
l_name = expandTable(pstate, l_rte->eref->relname, TRUE);
}
if (IsA(j->rarg, JoinExpr))
{
parseFromClause(pstate, lcons(j->rarg, NIL));
l_name = ((JoinExpr *) j->larg)->alias;
}
else
{
Assert(IsA(j->rarg, RangeVar));
r_rte = transformTableEntry(pstate, (RangeVar *) j->rarg);
r_name = expandTable(pstate, r_rte->eref->relname, TRUE);
}
/*
* Natural join does not explicitly specify columns; must
* generate columns to join. Need to run through the list of
* columns from each table or join result and match up the
* column names. Use the first table, and check every column
* in the second table for a match.
*/
if (j->isNatural)
{
List *lx,
*rx;
List *rlist = NULL;
foreach(lx, l_name->attrs)
{
Ident *id = NULL;
Value *l_col = lfirst(lx);
Assert(IsA(l_col, String));
foreach(rx, r_name->attrs)
{
Value *r_col = lfirst(rx);
Assert(IsA(r_col, String));
if (strcmp(strVal(l_col), strVal(r_col)) == 0)
{
id = (Ident *) makeNode(Ident);
id->name = strVal(l_col);
break;
}
}
/* right column matched? then keep as join column... */
if (id != NULL)
rlist = lappend(rlist, id);
}
j->quals = rlist;
printf("NATURAL JOIN columns are %s\n", nodeToString(rlist));
}
if (j->jointype == INNER_P)
{
/* CROSS JOIN */
if (j->quals == NULL)
printf("CROSS JOIN...\n");
/*
* JOIN/USING This is an inner join, so rip apart the join
* node and transform into a traditional FROM list.
* NATURAL JOIN and JOIN USING both change the shape of
* the result. Need to generate a list of result columns
* to use for target list expansion and validation.
*/
else if (IsA(j->quals, List))
{
/*
* List of Ident nodes means column names from a real
* USING clause. Determine the shape of the joined
* table.
*/
List *ucols,
*ucol;
List *shape = NULL;
List *alias = NULL;
List *l_shape,
*r_shape;
List *l_cols = makeAttrList(l_name);
List *r_cols = makeAttrList(r_name);
printf("USING input tables are:\n %s\n %s\n",
nodeToString(l_name), nodeToString(r_name));
printf("USING expanded tables are:\n %s\n %s\n",
nodeToString(l_cols), nodeToString(r_cols));
/* Columns from the USING clause... */
ucols = (List *) j->quals;
foreach(ucol, ucols)
{
List *col;
Attr *l_attr = NULL,
*r_attr = NULL;
Ident *id = lfirst(ucol);
Attr *attr = makeAttr("", id->name);
foreach(col, l_cols)
{
attr = lfirst(col);
if (strcmp(AttrString(attr), id->name) == 0)
{
l_attr = attr;
break;
}
}
foreach(col, r_cols)
{
attr = lfirst(col);
if (strcmp(AttrString(attr), id->name) == 0)
{
r_attr = attr;
break;
}
}
if (l_attr == NULL)
elog(ERROR, "USING column '%s' not found in table '%s'",
id->name, l_name->relname);
if (r_attr == NULL)
elog(ERROR, "USING column '%s' not found in table '%s'",
id->name, r_name->relname);
shape = lappend(shape, l_attr);
alias = lappend(alias, makeAttr("", AttrString(l_attr)));
}
printf("JOIN/USING join columns are %s\n", nodeToString(shape));
/* Remaining columns from the left side... */
l_shape = makeUniqueAttrList(makeAttrList(l_name), shape);
printf("JOIN/USING left columns are %s\n", nodeToString(l_shape));
r_shape = makeUniqueAttrList(makeAttrList(r_name), shape);
printf("JOIN/USING right columns are %s\n", nodeToString(r_shape));
printf("JOIN/USING input quals are %s\n", nodeToString(j->quals));
j->quals = transformUsingClause(pstate, shape, l_cols, r_cols);
printf("JOIN/USING transformed quals are %s\n", nodeToString(j->quals));
alias = nconc(nconc(alias, listCopy(l_shape)), listCopy(r_shape));
shape = nconc(nconc(shape, l_shape), r_shape);
printf("JOIN/USING shaped table is %s\n", nodeToString(shape));
printf("JOIN/USING alias list is %s\n", nodeToString(alias));
pstate->p_shape = shape;
pstate->p_alias = alias;
}
/* otherwise, must be an expression from an ON clause... */
else
j->quals = (List *) lcons(j->quals, NIL);
/* listCopy may not be needed here --- will j->quals list
* be used again anywhere? The #ifdef'd code below may need
* it, if it ever gets used...
*/
pstate->p_join_quals = nconc(pstate->p_join_quals,
listCopy(j->quals));
#if 0
if (qual == NULL)
elog(ERROR, "JOIN/ON not supported in this context");
printf("Table aliases are %s\n", nodeToString(*aliasList));
#endif
#if 0
/* XXX this code is WRONG because j->quals is a List
* not a simple expression. Perhaps *qual
* ought also to be a List and we append to it,
* similarly to the way p_join_quals is handled above?
*/
if (*qual == NULL)
{
/* merge qualified join clauses... */
if (j->quals != NULL)
{
if (*qual != NULL)
{
A_Expr *a = makeNode(A_Expr);
a->oper = AND;
a->opname = NULL;
a->lexpr = (Node *) *qual;
a->rexpr = (Node *) j->quals;
*qual = (Node *) a;
}
else
*qual = (Node *) j->quals;
}
}
else
{
elog(ERROR, "Multiple JOIN/ON clauses not handled (internal error)");
*qual = lappend(*qual, j->quals);
}
#endif
/*
* if we are transforming this node back into a FROM list,
* then we will need to replace the node with two nodes.
* Will need access to the previous list item to change
* the link pointer to reference these new nodes. Try
* accumulating and returning a new list. - thomas
* 1999-01-08 Not doing this yet though!
*/
}
else if ((j->jointype == LEFT)
|| (j->jointype == RIGHT)
|| (j->jointype == FULL))
elog(ERROR, "OUTER JOIN is not yet supported");
else
elog(ERROR, "Unrecognized JOIN clause; tag is %d (internal error)",
j->jointype);
#else
elog(ERROR, "JOIN expressions are not yet implemented");
#endif
}
else
elog(ERROR, "parseFromClause: unexpected FROM clause node (internal error)"
"\n\t%s", nodeToString(n));
}
} /* parseFromClause() */
/*
* findTargetlistEntry -
* Returns the targetlist entry matching the given (untransformed) node.
* If no matching entry exists, one is created and appended to the target
* list as a "resjunk" node.
*
* node the ORDER BY, GROUP BY, or DISTINCT ON expression to be matched
* tlist the existing target list (NB: this will never be NIL, which is a
* good thing since we'd be unable to append to it if it were...)
* clause identifies clause type being processed.
*/
static TargetEntry *
findTargetlistEntry(ParseState *pstate, Node *node, List *tlist, int clause)
{
TargetEntry *target_result = NULL;
List *tl;
Node *expr;
/*----------
* Handle two special cases as mandated by the SQL92 spec:
*
* 1. Bare ColumnName (no qualifier or subscripts)
* For a bare identifier, we search for a matching column name
* in the existing target list. Multiple matches are an error
* unless they refer to identical values; for example,
* we allow SELECT a, a FROM table ORDER BY a
* but not SELECT a AS b, b FROM table ORDER BY b
* If no match is found, we fall through and treat the identifier
* as an expression.
* For GROUP BY, it is incorrect to match the grouping item against
* targetlist entries: according to SQL92, an identifier in GROUP BY
* is a reference to a column name exposed by FROM, not to a target
* list column. However, many implementations (including pre-7.0
* PostgreSQL) accept this anyway. So for GROUP BY, we look first
* to see if the identifier matches any FROM column name, and only
* try for a targetlist name if it doesn't. This ensures that we
* adhere to the spec in the case where the name could be both.
* DISTINCT ON isn't in the standard, so we can do what we like there;
* we choose to make it work like ORDER BY, on the rather flimsy
* grounds that ordinary DISTINCT works on targetlist entries.
*
* 2. IntegerConstant
* This means to use the n'th item in the existing target list.
* Note that it would make no sense to order/group/distinct by an
* actual constant, so this does not create a conflict with our
* extension to order/group by an expression.
* GROUP BY column-number is not allowed by SQL92, but since
* the standard has no other behavior defined for this syntax,
* we may as well accept this common extension.
*
* Note that pre-existing resjunk targets must not be used in either case,
* since the user didn't write them in his SELECT list.
*
* If neither special case applies, fall through to treat the item as
* an expression.
*----------
*/
if (IsA(node, Ident) &&((Ident *) node)->indirection == NIL)
{
char *name = ((Ident *) node)->name;
if (clause == GROUP_CLAUSE)
{
/*
* In GROUP BY, we must prefer a match against a FROM-clause
* column to one against the targetlist. Look to see if there
* is a matching column. If so, fall through to let
* transformExpr() do the rest. NOTE: if name could refer
* ambiguously to more than one column name exposed by FROM,
* colnameRangeTableEntry will elog(ERROR). That's just what
* we want here.
*/
if (colnameRangeTableEntry(pstate, name) != NULL)
name = NULL;
}
if (name != NULL)
{
foreach(tl, tlist)
{
TargetEntry *tle = (TargetEntry *) lfirst(tl);
Resdom *resnode = tle->resdom;
if (!resnode->resjunk &&
strcmp(resnode->resname, name) == 0)
{
if (target_result != NULL)
{
if (!equal(target_result->expr, tle->expr))
elog(ERROR, "%s '%s' is ambiguous",
clauseText[clause], name);
}
else
target_result = tle;
/* Stay in loop to check for ambiguity */
}
}
if (target_result != NULL)
return target_result; /* return the first match */
}
}
if (IsA(node, A_Const))
{
Value *val = &((A_Const *) node)->val;
int targetlist_pos = 0;
int target_pos;
if (!IsA(val, Integer))
elog(ERROR, "Non-integer constant in %s", clauseText[clause]);
target_pos = intVal(val);
foreach(tl, tlist)
{
TargetEntry *tle = (TargetEntry *) lfirst(tl);
Resdom *resnode = tle->resdom;
if (!resnode->resjunk)
{
if (++targetlist_pos == target_pos)
return tle; /* return the unique match */
}
}
elog(ERROR, "%s position %d is not in target list",
clauseText[clause], target_pos);
}
/*
* Otherwise, we have an expression (this is a Postgres extension not
* found in SQL92). Convert the untransformed node to a transformed
* expression, and search for a match in the tlist. NOTE: it doesn't
* really matter whether there is more than one match. Also, we are
* willing to match a resjunk target here, though the above cases must
* ignore resjunk targets.
*/
expr = transformExpr(pstate, node, EXPR_COLUMN_FIRST);
foreach(tl, tlist)
{
TargetEntry *tle = (TargetEntry *) lfirst(tl);
if (equal(expr, tle->expr))
return tle;
}
/*
* If no matches, construct a new target entry which is appended to
* the end of the target list. This target is given resjunk = TRUE so
* that it will not be projected into the final tuple.
*/
target_result = transformTargetEntry(pstate, node, expr, NULL, true);
lappend(tlist, target_result);
return target_result;
}
/*
* transformGroupClause -
* transform a Group By clause
*
*/
List *
transformGroupClause(ParseState *pstate, List *grouplist, List *targetlist)
{
List *glist = NIL,
*gl;
foreach(gl, grouplist)
{
TargetEntry *tle;
tle = findTargetlistEntry(pstate, lfirst(gl),
targetlist, GROUP_CLAUSE);
/* avoid making duplicate grouplist entries */
if (!exprIsInSortList(tle->expr, glist, targetlist))
{
GroupClause *grpcl = makeNode(GroupClause);
grpcl->tleSortGroupRef = assignSortGroupRef(tle, targetlist);
grpcl->sortop = oprid(oper("<",
tle->resdom->restype,
tle->resdom->restype, false));
glist = lappend(glist, grpcl);
}
}
return glist;
}
/*
* transformSortClause -
* transform an ORDER BY clause
*/
List *
transformSortClause(ParseState *pstate,
List *orderlist,
List *targetlist)
{
List *sortlist = NIL;
List *olitem;
foreach(olitem, orderlist)
{
SortGroupBy *sortby = lfirst(olitem);
TargetEntry *tle;
tle = findTargetlistEntry(pstate, sortby->node,
targetlist, ORDER_CLAUSE);
sortlist = addTargetToSortList(tle, sortlist, targetlist,
sortby->useOp);
}
return sortlist;
}
/*
* transformDistinctClause -
* transform a DISTINCT or DISTINCT ON clause
*
* Since we may need to add items to the query's sortClause list, that list
* is passed by reference. We might also need to add items to the query's
* targetlist, but we assume that cannot be empty initially, so we can
* lappend to it even though the pointer is passed by value.
*/
List *
transformDistinctClause(ParseState *pstate, List *distinctlist,
List *targetlist, List **sortClause)
{
List *result = NIL;
List *slitem;
List *dlitem;
/* No work if there was no DISTINCT clause */
if (distinctlist == NIL)
return NIL;
if (lfirst(distinctlist) == NIL)
{
/* We had SELECT DISTINCT */
/*
* All non-resjunk elements from target list that are not already
* in the sort list should be added to it. (We don't really care
* what order the DISTINCT fields are checked in, so we can leave
* the user's ORDER BY spec alone, and just add additional sort
* keys to it to ensure that all targetlist items get sorted.)
*/
*sortClause = addAllTargetsToSortList(*sortClause, targetlist);
/*
* Now, DISTINCT list consists of all non-resjunk sortlist items.
* Actually, all the sortlist items had better be non-resjunk!
* Otherwise, user wrote SELECT DISTINCT with an ORDER BY item
* that does not appear anywhere in the SELECT targetlist, and we
* can't implement that with only one sorting pass...
*/
foreach(slitem, *sortClause)
{
SortClause *scl = (SortClause *) lfirst(slitem);
TargetEntry *tle = get_sortgroupclause_tle(scl, targetlist);
if (tle->resdom->resjunk)
elog(ERROR, "For SELECT DISTINCT, ORDER BY expressions must appear in target list");
else
result = lappend(result, copyObject(scl));
}
}
else
{
/* We had SELECT DISTINCT ON (expr, ...) */
/*
* If the user writes both DISTINCT ON and ORDER BY, then the two
* expression lists must match (until one or the other runs out).
* Otherwise the ORDER BY requires a different sort order than the
* DISTINCT does, and we can't implement that with only one sort
* pass (and if we do two passes, the results will be rather
* unpredictable). However, it's OK to have more DISTINCT ON
* expressions than ORDER BY expressions; we can just add the
* extra DISTINCT values to the sort list, much as we did above
* for ordinary DISTINCT fields.
*
* Actually, it'd be OK for the common prefixes of the two lists to
* match in any order, but implementing that check seems like more
* trouble than it's worth.
*/
List *nextsortlist = *sortClause;
foreach(dlitem, distinctlist)
{
TargetEntry *tle;
tle = findTargetlistEntry(pstate, lfirst(dlitem),
targetlist, DISTINCT_ON_CLAUSE);
if (nextsortlist != NIL)
{
SortClause *scl = (SortClause *) lfirst(nextsortlist);
if (tle->resdom->ressortgroupref != scl->tleSortGroupRef)
elog(ERROR, "SELECT DISTINCT ON expressions must match initial ORDER BY expressions");
result = lappend(result, copyObject(scl));
nextsortlist = lnext(nextsortlist);
}
else
{
*sortClause = addTargetToSortList(tle, *sortClause,
targetlist, NULL);
/*
* Probably, the tle should always have been added at the
* end of the sort list ... but search to be safe.
*/
foreach(slitem, *sortClause)
{
SortClause *scl = (SortClause *) lfirst(slitem);
if (tle->resdom->ressortgroupref == scl->tleSortGroupRef)
{
result = lappend(result, copyObject(scl));
break;
}
}
if (slitem == NIL)
elog(ERROR, "transformDistinctClause: failed to add DISTINCT ON clause to target list");
}
}
}
return result;
}
/*
* addAllTargetsToSortList
* Make sure all non-resjunk targets in the targetlist are in the
* ORDER BY list, adding the not-yet-sorted ones to the end of the list.
* This is typically used to help implement SELECT DISTINCT.
*
* Returns the updated ORDER BY list.
*/
List *
addAllTargetsToSortList(List *sortlist, List *targetlist)
{
List *i;
foreach(i, targetlist)
{
TargetEntry *tle = (TargetEntry *) lfirst(i);
if (!tle->resdom->resjunk)
sortlist = addTargetToSortList(tle, sortlist, targetlist, NULL);
}
return sortlist;
}
/*
* addTargetToSortList
* If the given targetlist entry isn't already in the ORDER BY list,
* add it to the end of the list, using the sortop with given name
* or any available sort operator if opname == NULL.
*
* Returns the updated ORDER BY list.
*/
static List *
addTargetToSortList(TargetEntry *tle, List *sortlist, List *targetlist,
char *opname)
{
/* avoid making duplicate sortlist entries */
if (!exprIsInSortList(tle->expr, sortlist, targetlist))
{
SortClause *sortcl = makeNode(SortClause);
sortcl->tleSortGroupRef = assignSortGroupRef(tle, targetlist);
if (opname)
sortcl->sortop = oprid(oper(opname,
tle->resdom->restype,
tle->resdom->restype, false));
else
sortcl->sortop = any_ordering_op(tle->resdom->restype);
sortlist = lappend(sortlist, sortcl);
}
return sortlist;
}
/*
* assignSortGroupRef
* Assign the targetentry an unused ressortgroupref, if it doesn't
* already have one. Return the assigned or pre-existing refnumber.
*
* 'tlist' is the targetlist containing (or to contain) the given targetentry.
*/
Index
assignSortGroupRef(TargetEntry *tle, List *tlist)
{
Index maxRef;
List *l;
if (tle->resdom->ressortgroupref) /* already has one? */
return tle->resdom->ressortgroupref;
/* easiest way to pick an unused refnumber: max used + 1 */
maxRef = 0;
foreach(l, tlist)
{
Index ref = ((TargetEntry *) lfirst(l))->resdom->ressortgroupref;
if (ref > maxRef)
maxRef = ref;
}
tle->resdom->ressortgroupref = maxRef + 1;
return tle->resdom->ressortgroupref;
}
/*
* exprIsInSortList
* Is the given expression already in the sortlist?
* Note we will say 'yes' if it is equal() to any sortlist item,
* even though that might be a different targetlist member.
*
* Works for both SortClause and GroupClause lists.
*/
static bool
exprIsInSortList(Node *expr, List *sortList, List *targetList)
{
List *i;
foreach(i, sortList)
{
SortClause *scl = (SortClause *) lfirst(i);
if (equal(expr, get_sortgroupclause_expr(scl, targetList)))
return true;
}
return false;
}
/* transformUnionClause()
* Transform a UNION clause.
* Note that the union clause is actually a fully-formed select structure.
* So, it is evaluated as a select, then the resulting target fields
* are matched up to ensure correct types in the results.
* The select clause parsing is done recursively, so the unions are evaluated
* right-to-left. One might want to look at all columns from all clauses before
* trying to coerce, but unless we keep track of the call depth we won't know
* when to do this because of the recursion.
* Let's just try matching in pairs for now (right to left) and see if it works.
* - thomas 1998-05-22
*/
#ifdef NOT_USED
static List *
transformUnionClause(List *unionClause, List *targetlist)
{
List *union_list = NIL;
List *qlist,
*qlist_item;
if (unionClause)
{
/* recursion */
qlist = parse_analyze(unionClause, NULL);
foreach(qlist_item, qlist)
{
Query *query = (Query *) lfirst(qlist_item);
List *prev_target = targetlist;
List *next_target;
int prev_len = 0,
next_len = 0;
foreach(prev_target, targetlist)
if (!((TargetEntry *) lfirst(prev_target))->resdom->resjunk)
prev_len++;
foreach(next_target, query->targetList)
if (!((TargetEntry *) lfirst(next_target))->resdom->resjunk)
next_len++;
if (prev_len != next_len)
elog(ERROR, "Each UNION clause must have the same number of columns");
foreach(next_target, query->targetList)
{
Oid itype;
Oid otype;
otype = ((TargetEntry *) lfirst(prev_target))->resdom->restype;
itype = ((TargetEntry *) lfirst(next_target))->resdom->restype;
/* one or both is a NULL column? then don't convert... */
if (otype == InvalidOid)
{
/* propagate a known type forward, if available */
if (itype != InvalidOid)
((TargetEntry *) lfirst(prev_target))->resdom->restype = itype;
#if FALSE
else
{
((TargetEntry *) lfirst(prev_target))->resdom->restype = UNKNOWNOID;
((TargetEntry *) lfirst(next_target))->resdom->restype = UNKNOWNOID;
}
#endif
}
else if (itype == InvalidOid)
{
}
/* they don't match in type? then convert... */
else if (itype != otype)
{
Node *expr;
expr = ((TargetEntry *) lfirst(next_target))->expr;
expr = CoerceTargetExpr(NULL, expr, itype, otype, -1);
if (expr == NULL)
{
elog(ERROR, "Unable to transform %s to %s"
"\n\tEach UNION clause must have compatible target types",
typeidTypeName(itype),
typeidTypeName(otype));
}
((TargetEntry *) lfirst(next_target))->expr = expr;
((TargetEntry *) lfirst(next_target))->resdom->restype = otype;
}
/* both are UNKNOWN? then evaluate as text... */
else if (itype == UNKNOWNOID)
{
((TargetEntry *) lfirst(next_target))->resdom->restype = TEXTOID;
((TargetEntry *) lfirst(prev_target))->resdom->restype = TEXTOID;
}
prev_target = lnext(prev_target);
}
union_list = lappend(union_list, query);
}
return union_list;
}
else
return NIL;
}
#endif
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