Allow functions that return sets of tuples to return simple NULLs.

ExecMakeTableFunctionResult(), which is used in SELECT FROM function(...)
cases, formerly treated a simple NULL output from a function that both
returnsSet and returnsTuple as a violation of the SRF protocol.  What seems
better is to treat a NULL output as equivalent to ROW(NULL,NULL,...).
Without this, cases such as SELECT FROM unnest(...) on an array of
composite are vulnerable to unexpected and not-very-helpful failures.
Old code comments here suggested an alternative of just ignoring
simple-NULL outputs, but that doesn't seem very principled.

This change had been hung up for a long time due to uncertainty about
how much we wanted to buy into the equivalence of simple NULL and
ROW(NULL,NULL,...).  I think that's been mostly resolved by the discussion
around bug #14235, so let's go ahead and do it.

Per bug #7808 from Joe Van Dyk.  Although this is a pretty old report,
fixing it smells a bit more like a new feature than a bug fix, and the
lack of other similar complaints suggests that we shouldn't take much risk
of destabilization by back-patching.  (Maybe that could be revisited once
this patch has withstood some field usage.)

Andrew Gierth and Tom Lane

Report: <E1TurJE-0006Es-TK@wrigleys.postgresql.org>

diff --git a/src/backend/executor/execQual.c b/src/backend/executor/execQual.c
index 2b9102125ef5302e9ad5e4341379dbbcece59152..69bf65d00bf97a71d7a6ab4781ccb117cd04cb32 100644 (file)
--- a/src/backend/executor/execQual.c
+++ b/src/backend/executor/execQual.c
@@ -2229,45 +2229,16 @@ ExecMakeTableFunctionResult(ExprState *funcexpr,
                break;
 
            /*
-            * Can't do anything very useful with NULL rowtype values. For a
-            * function returning set, we consider this a protocol violation
-            * (but another alternative would be to just ignore the result and
-            * "continue" to get another row).  For a function not returning
-            * set, we fall out of the loop; we'll cons up an all-nulls result
-            * row below.
-            */
-           if (returnsTuple && fcinfo.isnull)
-           {
-               if (!returnsSet)
-                   break;
-               ereport(ERROR,
-                       (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
-                        errmsg("function returning set of rows cannot return null value")));
-           }
-
-           /*
-            * If first time through, build tupdesc and tuplestore for result
+            * If first time through, build tuplestore for result.  For a
+            * scalar function result type, also make a suitable tupdesc.
             */
            if (first_time)
            {
                oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_query_memory);
-               if (returnsTuple)
-               {
-                   /*
-                    * Use the type info embedded in the rowtype Datum to look
-                    * up the needed tupdesc.  Make a copy for the query.
-                    */
-                   HeapTupleHeader td;
-
-                   td = DatumGetHeapTupleHeader(result);
-                   tupdesc = lookup_rowtype_tupdesc_copy(HeapTupleHeaderGetTypeId(td),
-                                              HeapTupleHeaderGetTypMod(td));
-               }
-               else
+               tupstore = tuplestore_begin_heap(randomAccess, false, work_mem);
+               rsinfo.setResult = tupstore;
+               if (!returnsTuple)
                {
-                   /*
-                    * Scalar type, so make a single-column descriptor
-                    */
                    tupdesc = CreateTemplateTupleDesc(1, false);
                    TupleDescInitEntry(tupdesc,
                                       (AttrNumber) 1,
@@ -2275,11 +2246,9 @@ ExecMakeTableFunctionResult(ExprState *funcexpr,
                                       funcrettype,
                                       -1,
                                       0);
+                   rsinfo.setDesc = tupdesc;
                }
-               tupstore = tuplestore_begin_heap(randomAccess, false, work_mem);
                MemoryContextSwitchTo(oldcontext);
-               rsinfo.setResult = tupstore;
-               rsinfo.setDesc = tupdesc;
            }
 
            /*
@@ -2287,31 +2256,69 @@ ExecMakeTableFunctionResult(ExprState *funcexpr,
             */
            if (returnsTuple)
            {
-               HeapTupleHeader td;
+               if (!fcinfo.isnull)
+               {
+                   HeapTupleHeader td = DatumGetHeapTupleHeader(result);
 
-               td = DatumGetHeapTupleHeader(result);
+                   if (tupdesc == NULL)
+                   {
+                       /*
+                        * This is the first non-NULL result from the
+                        * function.  Use the type info embedded in the
+                        * rowtype Datum to look up the needed tupdesc.  Make
+                        * a copy for the query.
+                        */
+                       oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_query_memory);
+                       tupdesc = lookup_rowtype_tupdesc_copy(HeapTupleHeaderGetTypeId(td),
+                                              HeapTupleHeaderGetTypMod(td));
+                       rsinfo.setDesc = tupdesc;
+                       MemoryContextSwitchTo(oldcontext);
+                   }
+                   else
+                   {
+                       /*
+                        * Verify all later returned rows have same subtype;
+                        * necessary in case the type is RECORD.
+                        */
+                       if (HeapTupleHeaderGetTypeId(td) != tupdesc->tdtypeid ||
+                           HeapTupleHeaderGetTypMod(td) != tupdesc->tdtypmod)
+                           ereport(ERROR,
+                                   (errcode(ERRCODE_DATATYPE_MISMATCH),
+                                    errmsg("rows returned by function are not all of the same row type")));
+                   }
 
-               /*
-                * Verify all returned rows have same subtype; necessary in
-                * case the type is RECORD.
-                */
-               if (HeapTupleHeaderGetTypeId(td) != tupdesc->tdtypeid ||
-                   HeapTupleHeaderGetTypMod(td) != tupdesc->tdtypmod)
-                   ereport(ERROR,
-                           (errcode(ERRCODE_DATATYPE_MISMATCH),
-                            errmsg("rows returned by function are not all of the same row type")));
+                   /*
+                    * tuplestore_puttuple needs a HeapTuple not a bare
+                    * HeapTupleHeader, but it doesn't need all the fields.
+                    */
+                   tmptup.t_len = HeapTupleHeaderGetDatumLength(td);
+                   tmptup.t_data = td;
 
-               /*
-                * tuplestore_puttuple needs a HeapTuple not a bare
-                * HeapTupleHeader, but it doesn't need all the fields.
-                */
-               tmptup.t_len = HeapTupleHeaderGetDatumLength(td);
-               tmptup.t_data = td;
+                   tuplestore_puttuple(tupstore, &tmptup);
+               }
+               else
+               {
+                   /*
+                    * NULL result from a tuple-returning function; expand it
+                    * to a row of all nulls.  We rely on the expectedDesc to
+                    * form such rows.  (Note: this would be problematic if
+                    * tuplestore_putvalues saved the tdtypeid/tdtypmod from
+                    * the provided descriptor, since that might not match
+                    * what we get from the function itself.  But it doesn't.)
+                    */
+                   int         natts = expectedDesc->natts;
+                   bool       *nullflags;
 
-               tuplestore_puttuple(tupstore, &tmptup);
+                   nullflags = (bool *) palloc(natts * sizeof(bool));
+                   memset(nullflags, true, natts * sizeof(bool));
+                   tuplestore_putvalues(tupstore, expectedDesc, NULL, nullflags);
+               }
            }
            else
+           {
+               /* Scalar-type case: just store the function result */
                tuplestore_putvalues(tupstore, tupdesc, &result, &fcinfo.isnull);
+           }
 
            /*
             * Are we done?
@@ -2343,7 +2350,8 @@ no_function_result:
    /*
     * If we got nothing from the function (ie, an empty-set or NULL result),
     * we have to create the tuplestore to return, and if it's a
-    * non-set-returning function then insert a single all-nulls row.
+    * non-set-returning function then insert a single all-nulls row.  As
+    * above, we depend on the expectedDesc to manufacture the dummy row.
     */
    if (rsinfo.setResult == NULL)
    {
@@ -2353,15 +2361,12 @@ no_function_result:
        if (!returnsSet)
        {
            int         natts = expectedDesc->natts;
-           Datum      *nulldatums;
            bool       *nullflags;
 
            MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
-           nulldatums = (Datum *) palloc0(natts * sizeof(Datum));
            nullflags = (bool *) palloc(natts * sizeof(bool));
            memset(nullflags, true, natts * sizeof(bool));
-           MemoryContextSwitchTo(econtext->ecxt_per_query_memory);
-           tuplestore_putvalues(tupstore, expectedDesc, nulldatums, nullflags);
+           tuplestore_putvalues(tupstore, expectedDesc, NULL, nullflags);
        }
    }
 

diff --git a/src/test/regress/expected/rangefuncs.out b/src/test/regress/expected/rangefuncs.out
index 00ef4210549879668afa69344e8b51bccbfb3afb..f06cfa4b21dc470a3ae1dc86857e4167bc3f736f 100644 (file)
--- a/src/test/regress/expected/rangefuncs.out
+++ b/src/test/regress/expected/rangefuncs.out
@@ -2076,3 +2076,33 @@ select x from int8_tbl, extractq2_2_opt(int8_tbl) f(x);
  -4567890123456789
 (5 rows)
 
+-- check handling of nulls in SRF results (bug #7808)
+create type foo2 as (a integer, b text);
+select *, row_to_json(u) from unnest(array[(1,'foo')::foo2, null::foo2]) u;
+ a |  b  |     row_to_json     
+---+-----+---------------------
+ 1 | foo | {"a":1,"b":"foo"}
+   |     | {"a":null,"b":null}
+(2 rows)
+
+select *, row_to_json(u) from unnest(array[null::foo2, null::foo2]) u;
+ a | b |     row_to_json     
+---+---+---------------------
+   |   | {"a":null,"b":null}
+   |   | {"a":null,"b":null}
+(2 rows)
+
+select *, row_to_json(u) from unnest(array[null::foo2, (1,'foo')::foo2, null::foo2]) u;
+ a |  b  |     row_to_json     
+---+-----+---------------------
+   |     | {"a":null,"b":null}
+ 1 | foo | {"a":1,"b":"foo"}
+   |     | {"a":null,"b":null}
+(3 rows)
+
+select *, row_to_json(u) from unnest(array[]::foo2[]) u;
+ a | b | row_to_json 
+---+---+-------------
+(0 rows)
+
+drop type foo2;

diff --git a/src/test/regress/sql/rangefuncs.sql b/src/test/regress/sql/rangefuncs.sql
index 9484023f97b79531c11faba7e3dc730b58eb6f75..c8edc553bc39c7b64d6521b86c4ce038348b776b 100644 (file)
--- a/src/test/regress/sql/rangefuncs.sql
+++ b/src/test/regress/sql/rangefuncs.sql
@@ -639,3 +639,14 @@ explain (verbose, costs off)
 select x from int8_tbl, extractq2_2_opt(int8_tbl) f(x);
 
 select x from int8_tbl, extractq2_2_opt(int8_tbl) f(x);
+
+-- check handling of nulls in SRF results (bug #7808)
+
+create type foo2 as (a integer, b text);
+
+select *, row_to_json(u) from unnest(array[(1,'foo')::foo2, null::foo2]) u;
+select *, row_to_json(u) from unnest(array[null::foo2, null::foo2]) u;
+select *, row_to_json(u) from unnest(array[null::foo2, (1,'foo')::foo2, null::foo2]) u;
+select *, row_to_json(u) from unnest(array[]::foo2[]) u;
+
+drop type foo2;