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Improve handling of "UPDATE ... SET (column_list) = row_constructor".

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Previously, the right-hand side of a multiple-column assignment, if it
wasn't a sub-SELECT, had to be a simple parenthesized expression list,
because gram.y was responsible for "bursting" the construct into
independent column assignments.  This had the minor defect that you
couldn't write ROW (though you should be able to, since the standard says
this is a row constructor), and the rather larger defect that unlike other
uses of row constructors, we would not expand a "foo.*" item into multiple
columns.

Fix that by changing the RHS to be just "a_expr" in the grammar, leaving
it to transformMultiAssignRef to separate the elements of a RowExpr;
which it will do only after performing standard transformation of the
RowExpr, so that "foo.*" behaves as expected.

The key reason we didn't do that before was the hard-wired handling of
DEFAULT tokens (SetToDefault nodes).  This patch deals with that issue by
allowing DEFAULT in any a_expr and having parse analysis throw an error
if SetToDefault is found in an unexpected place.  That's an improvement
anyway since the error can be more specific than just "syntax error".

The SQL standard suggests that the RHS could be any a_expr yielding a
suitable row value.  This patch doesn't really move the goal posts in that
respect --- you're still limited to RowExpr or a sub-SELECT --- but it does
fix the grammar restriction, so it provides some tangible progress towards
a full implementation.  And the limitation is now documented by an explicit
error message rather than an unhelpful "syntax error".

Discussion: <8542.1479742008@sss.pgh.pa.us>
This commit is contained in:
Tom Lane
2016-11-22 15:19:57 -05:00
parent e8ac886c24
commit 906bfcad7b
8 changed files with 229 additions and 181 deletions
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35
src/backend/parser/analyze.c
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@@ -644,8 +644,12 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt)
{
List *sublist = (List *) lfirst(lc);
/* Do basic expression transformation (same as a ROW() expr) */
sublist = transformExpressionList(pstate, sublist, EXPR_KIND_VALUES);
/*
* Do basic expression transformation (same as a ROW() expr, but
* allow SetToDefault at top level)
*/
sublist = transformExpressionList(pstate, sublist,
EXPR_KIND_VALUES, true);
/*
* All the sublists must be the same length, *after*
@@ -752,10 +756,14 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt)
Assert(list_length(valuesLists) == 1);
Assert(selectStmt->intoClause == NULL);
/* Do basic expression transformation (same as a ROW() expr) */
/*
* Do basic expression transformation (same as a ROW() expr, but allow
* SetToDefault at top level)
*/
exprList = transformExpressionList(pstate,
(List *) linitial(valuesLists),
EXPR_KIND_VALUES);
EXPR_KIND_VALUES,
true);
/* Prepare row for assignment to target table */
exprList = transformInsertRow(pstate, exprList,
@@ -1293,9 +1301,7 @@ transformValuesClause(ParseState *pstate, SelectStmt *stmt)
}
/*
* For each row of VALUES, transform the raw expressions. This is also a
* handy place to reject DEFAULT nodes, which the grammar allows for
* simplicity.
* For each row of VALUES, transform the raw expressions.
*
* Note that the intermediate representation we build is column-organized
* not row-organized. That simplifies the type and collation processing
@@ -1305,8 +1311,12 @@ transformValuesClause(ParseState *pstate, SelectStmt *stmt)
{
List *sublist = (List *) lfirst(lc);
/* Do basic expression transformation (same as a ROW() expr) */
sublist = transformExpressionList(pstate, sublist, EXPR_KIND_VALUES);
/*
* Do basic expression transformation (same as a ROW() expr, but here
* we disallow SetToDefault)
*/
sublist = transformExpressionList(pstate, sublist,
EXPR_KIND_VALUES, false);
/*
* All the sublists must be the same length, *after* transformation
@@ -1329,17 +1339,12 @@ transformValuesClause(ParseState *pstate, SelectStmt *stmt)
exprLocation((Node *) sublist))));
}
/* Check for DEFAULT and build per-column expression lists */
/* Build per-column expression lists */
i = 0;
foreach(lc2, sublist)
{
Node *col = (Node *) lfirst(lc2);
if (IsA(col, SetToDefault))
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("DEFAULT can only appear in a VALUES list within INSERT"),
parser_errposition(pstate, exprLocation(col))));
colexprs[i] = lappend(colexprs[i], col);
i++;
}