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Fix reporting of column typmods for multi-row VALUES constructs.

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expandRTE() and get_rte_attribute_type() reported the exprType() and
exprTypmod() values of the expressions in the first row of the VALUES as
being the column type/typmod returned by the VALUES RTE.  That's fine for
the data type, since we coerce all expressions in a column to have the same
common type.  But we don't coerce them to have a common typmod, so it was
possible for rows after the first one to return values that violate the
claimed column typmod.  This leads to the incorrect result seen in bug
#14448 from Hassan Mahmood, as well as some other corner-case misbehaviors.

The desired behavior is the same as we use in other type-unification
cases: report the common typmod if there is one, but otherwise return -1
indicating no particular constraint.

We fixed this in HEAD by deriving the typmods during transformValuesClause
and storing them in the RTE, but that's not a feasible solution in the back
branches.  Instead, just use a brute-force approach of determining the
correct common typmod during expandRTE() and get_rte_attribute_type().
Simple testing says that that doesn't really cost much, at least not in
common cases where expandRTE() is only used once per query.  It turns out
that get_rte_attribute_type() is typically never used at all on VALUES
RTEs, so the inefficiency there is of no great concern.

Report: https://postgr.es/m/20161205143037.4377.60754@wrigleys.postgresql.org
Discussion: https://postgr.es/m/27429.1480968538@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2016-12-09 12:01:14 -05:00
parent 79c89f1f4e
commit cf22c8cb89
3 changed files with 147 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

101
src/backend/parser/parse_relation.c
View File

@@ -52,6 +52,7 @@ static void expandTupleDesc(TupleDesc tupdesc, Alias *eref,
int rtindex, int sublevels_up,
int location, bool include_dropped,
List **colnames, List **colvars);
static int32 *getValuesTypmods(RangeTblEntry *rte);
static int specialAttNum(const char *attname);
static bool isQueryUsingTempRelation_walker(Node *node, void *context);
@@ -2157,9 +2158,22 @@ expandRTE(RangeTblEntry *rte, int rtindex, int sublevels_up,
{
/* Values RTE */
ListCell *aliasp_item = list_head(rte->eref->colnames);
int32 *coltypmods;
ListCell *lcv;
ListCell *lcc;
/*
* It's okay to extract column types from the expressions in
* the first row, since all rows will have been coerced to the
* same types. Their typmods might not be the same though, so
* we potentially need to examine all rows to compute those.
* Column collations are pre-computed in values_collations.
*/
if (colvars)
coltypmods = getValuesTypmods(rte);
else
coltypmods = NULL;
varattno = 0;
forboth(lcv, (List *) linitial(rte->values_lists),
lcc, rte->values_collations)
@@ -2184,13 +2198,15 @@ expandRTE(RangeTblEntry *rte, int rtindex, int sublevels_up,
varnode = makeVar(rtindex, varattno,
exprType(col),
exprTypmod(col),
coltypmods[varattno - 1],
colcollation,
sublevels_up);
varnode->location = location;
*colvars = lappend(*colvars, varnode);
}
}
if (coltypmods)
pfree(coltypmods);
}
break;
case RTE_JOIN:
@@ -2296,6 +2312,8 @@ expandRTE(RangeTblEntry *rte, int rtindex, int sublevels_up,
varnode = makeVar(rtindex, varattno,
coltype, coltypmod, colcoll,
sublevels_up);
varnode->location = location;
*colvars = lappend(*colvars, varnode);
}
}
@@ -2412,6 +2430,74 @@ expandTupleDesc(TupleDesc tupdesc, Alias *eref, int count, int offset,
}
}
/*
* getValuesTypmods -- expandRTE subroutine
*
* Identify per-column typmods for the given VALUES RTE. Returns a
* palloc'd array.
*/
static int32 *
getValuesTypmods(RangeTblEntry *rte)
{
int32 *coltypmods;
List *firstrow;
int ncolumns,
nvalid,
i;
ListCell *lc;
Assert(rte->values_lists != NIL);
firstrow = (List *) linitial(rte->values_lists);
ncolumns = list_length(firstrow);
coltypmods = (int32 *) palloc(ncolumns * sizeof(int32));
nvalid = 0;
/* Collect the typmods from the first VALUES row */
i = 0;
foreach(lc, firstrow)
{
Node *col = (Node *) lfirst(lc);
coltypmods[i] = exprTypmod(col);
if (coltypmods[i] >= 0)
nvalid++;
i++;
}
/*
* Scan remaining rows; as soon as we have a non-matching typmod for a
* column, reset that typmod to -1. We can bail out early if all typmods
* become -1.
*/
if (nvalid > 0)
{
for_each_cell(lc, lnext(list_head(rte->values_lists)))
{
List *thisrow = (List *) lfirst(lc);
ListCell *lc2;
Assert(list_length(thisrow) == ncolumns);
i = 0;
foreach(lc2, thisrow)
{
Node *col = (Node *) lfirst(lc2);
if (coltypmods[i] >= 0 && coltypmods[i] != exprTypmod(col))
{
coltypmods[i] = -1;
nvalid--;
}
i++;
}
if (nvalid <= 0)
break;
}
}
return coltypmods;
}
/*
* expandRelAttrs -
* Workhorse for "*" expansion: produce a list of targetentries
@@ -2656,18 +2742,25 @@ get_rte_attribute_type(RangeTblEntry *rte, AttrNumber attnum,
break;
case RTE_VALUES:
{
/* Values RTE --- get type info from first sublist */
/* collation is stored separately, though */
/*
* Values RTE --- we can get type info from first sublist, but
* typmod may require scanning all sublists, and collation is
* stored separately. Using getValuesTypmods() is overkill,
* but this path is taken so seldom for VALUES that it's not
* worth writing extra code.
*/
List *collist = (List *) linitial(rte->values_lists);
Node *col;
int32 *coltypmods = getValuesTypmods(rte);
if (attnum < 1 || attnum > list_length(collist))
elog(ERROR, "values list %s does not have attribute %d",
rte->eref->aliasname, attnum);
col = (Node *) list_nth(collist, attnum - 1);
*vartype = exprType(col);
*vartypmod = exprTypmod(col);
*vartypmod = coltypmods[attnum - 1];
*varcollid = list_nth_oid(rte->values_collations, attnum - 1);
pfree(coltypmods);
}
break;
case RTE_JOIN: