Fix "cannot accept a set" error when only some arms of a CASE return a set.

In commit c1352052ef1d4eeb2eb1d822a207ddc2d106cb13, I implemented an
optimization that assumed that a function's argument expressions would
either always return a set (ie multiple rows), or always not.  This is
wrong however: we allow CASE expressions in which some arms return a set
of some type and others just return a scalar of that type.  There may be
other examples as well.  To fix, replace the run-time test of whether an
argument returned a set with a static precheck (expression_returns_set).
This adds a little bit of query startup overhead, but it seems barely
measurable.

Per bug #8228 from David Johnston.  This has been broken since 8.0,
so patch all supported branches.

diff --git a/src/backend/executor/execQual.c b/src/backend/executor/execQual.c
index 5c14b4aa2d3d5a24b2d73acc812fd9f9ebe5a7bf..0eba025ef9ae2b747eda025189b58174381edda5 100644 (file)
--- a/src/backend/executor/execQual.c
+++ b/src/backend/executor/execQual.c
@@ -1634,9 +1634,7 @@ tupledesc_match(TupleDesc dst_tupdesc, TupleDesc src_tupdesc)
  * init_fcache is presumed already run on the FuncExprState.
  *
  * This function handles the most general case, wherein the function or
- * one of its arguments might (or might not) return a set. If we find
- * no sets involved, we will change the FuncExprState's function pointer
- * to use a simpler method on subsequent calls.
+ * one of its arguments can return a set.
  */
 static Datum
 ExecMakeFunctionResult(FuncExprState *fcache,
@@ -1906,13 +1904,12 @@ restart:
        /*
         * Non-set case: much easier.
         *
-        * We change the ExprState function pointer to use the simpler
-        * ExecMakeFunctionResultNoSets on subsequent calls.  This amounts to
-        * assuming that no argument can return a set if it didn't do so the
-        * first time.
+        * In common cases, this code path is unreachable because we'd have
+        * selected ExecMakeFunctionResultNoSets instead.  However, it's
+        * possible to get here if an argument sometimes produces set results
+        * and sometimes scalar results.  For example, a CASE expression might
+        * call a set-returning function in only some of its arms.
         */
-       fcache->xprstate.evalfunc = (ExprStateEvalFunc) ExecMakeFunctionResultNoSets;
-
        if (isDone)
            *isDone = ExprSingleResult;
 
@@ -2371,10 +2368,22 @@ ExecEvalFunc(FuncExprState *fcache,
    init_fcache(func->funcid, func->inputcollid, fcache,
                econtext->ecxt_per_query_memory, true);
 
-   /* Go directly to ExecMakeFunctionResult on subsequent uses */
-   fcache->xprstate.evalfunc = (ExprStateEvalFunc) ExecMakeFunctionResult;
-
-   return ExecMakeFunctionResult(fcache, econtext, isNull, isDone);
+   /*
+    * We need to invoke ExecMakeFunctionResult if either the function itself
+    * or any of its input expressions can return a set.  Otherwise, invoke
+    * ExecMakeFunctionResultNoSets.  In either case, change the evalfunc
+    * pointer to go directly there on subsequent uses.
+    */
+   if (fcache->func.fn_retset || expression_returns_set((Node *) func->args))
+   {
+       fcache->xprstate.evalfunc = (ExprStateEvalFunc) ExecMakeFunctionResult;
+       return ExecMakeFunctionResult(fcache, econtext, isNull, isDone);
+   }
+   else
+   {
+       fcache->xprstate.evalfunc = (ExprStateEvalFunc) ExecMakeFunctionResultNoSets;
+       return ExecMakeFunctionResultNoSets(fcache, econtext, isNull, isDone);
+   }
 }
 
 /* ----------------------------------------------------------------
@@ -2394,10 +2403,22 @@ ExecEvalOper(FuncExprState *fcache,
    init_fcache(op->opfuncid, op->inputcollid, fcache,
                econtext->ecxt_per_query_memory, true);
 
-   /* Go directly to ExecMakeFunctionResult on subsequent uses */
-   fcache->xprstate.evalfunc = (ExprStateEvalFunc) ExecMakeFunctionResult;
-
-   return ExecMakeFunctionResult(fcache, econtext, isNull, isDone);
+   /*
+    * We need to invoke ExecMakeFunctionResult if either the function itself
+    * or any of its input expressions can return a set.  Otherwise, invoke
+    * ExecMakeFunctionResultNoSets.  In either case, change the evalfunc
+    * pointer to go directly there on subsequent uses.
+    */
+   if (fcache->func.fn_retset || expression_returns_set((Node *) op->args))
+   {
+       fcache->xprstate.evalfunc = (ExprStateEvalFunc) ExecMakeFunctionResult;
+       return ExecMakeFunctionResult(fcache, econtext, isNull, isDone);
+   }
+   else
+   {
+       fcache->xprstate.evalfunc = (ExprStateEvalFunc) ExecMakeFunctionResultNoSets;
+       return ExecMakeFunctionResultNoSets(fcache, econtext, isNull, isDone);
+   }
 }
 
 /* ----------------------------------------------------------------

diff --git a/src/test/regress/expected/rangefuncs.out b/src/test/regress/expected/rangefuncs.out
index a988dd01a12db65c04778b2b2e56984057a56387..9d40510ecdb2356d1d843d3159b58cf2398f600b 100644 (file)
--- a/src/test/regress/expected/rangefuncs.out
+++ b/src/test/regress/expected/rangefuncs.out
@@ -1992,3 +1992,17 @@ select * from foobar();  -- fail
 ERROR:  function return row and query-specified return row do not match
 DETAIL:  Returned row contains 3 attributes, but query expects 2.
 drop function foobar();
+-- check behavior when a function's input sometimes returns a set (bug #8228)
+SELECT *,
+  lower(CASE WHEN id = 2 THEN (regexp_matches(str, '^0*([1-9]\d+)$'))[1]
+        ELSE str
+        END)
+FROM
+  (VALUES (1,''), (2,'0000000049404'), (3,'FROM 10000000876')) v(id, str);
+ id |       str        |      lower       
+----+------------------+------------------
+  1 |                  | 
+  2 | 0000000049404    | 49404
+  3 | FROM 10000000876 | from 10000000876
+(3 rows)
+

diff --git a/src/test/regress/sql/rangefuncs.sql b/src/test/regress/sql/rangefuncs.sql
index ac2769fdba9a501039e6ee25fcdd13e34b816d71..07d2e1a490e6636882ff6db5a8e09861b13a2400 100644 (file)
--- a/src/test/regress/sql/rangefuncs.sql
+++ b/src/test/regress/sql/rangefuncs.sql
@@ -599,3 +599,12 @@ $$ select (1, 2.1, 3) $$ language sql;
 select * from foobar();  -- fail
 
 drop function foobar();
+
+-- check behavior when a function's input sometimes returns a set (bug #8228)
+
+SELECT *,
+  lower(CASE WHEN id = 2 THEN (regexp_matches(str, '^0*([1-9]\d+)$'))[1]
+        ELSE str
+        END)
+FROM
+  (VALUES (1,''), (2,'0000000049404'), (3,'FROM 10000000876')) v(id, str);