Improve error message for the case where a requested foreign key constraint

does match some unique index on the referenced table, but that index is
only deferrably unique.  We were doing this nicely for the
default-to-primary-key case, but were being lazy for the other case.

Dean Rasheed

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 30a5c8b4546c0118f3a7fdda00a4436600eedd4b..7029c3c1e8cd3b98e9d103c77f7c57dab88a3ec1 100644 (file)
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -5117,6 +5117,7 @@ transformFkeyCheckAttrs(Relation pkrel,
 {
        Oid                     indexoid = InvalidOid;
        bool            found = false;
+       bool            found_deferrable = false;
        List       *indexoidlist;
        ListCell   *indexoidscan;
 
@@ -5143,12 +5144,11 @@ transformFkeyCheckAttrs(Relation pkrel,
                indexStruct = (Form_pg_index) GETSTRUCT(indexTuple);
 
                /*
-                * Must have the right number of columns; must be unique (non
-                * deferrable) and not a partial index; forget it if there are any
-                * expressions, too
+                * Must have the right number of columns; must be unique and not a
+                * partial index; forget it if there are any expressions, too
                 */
                if (indexStruct->indnatts == numattrs &&
-                       indexStruct->indisunique && indexStruct->indimmediate &&
+                       indexStruct->indisunique &&
                        heap_attisnull(indexTuple, Anum_pg_index_indpred) &&
                        heap_attisnull(indexTuple, Anum_pg_index_indexprs))
                {
@@ -5198,6 +5198,21 @@ transformFkeyCheckAttrs(Relation pkrel,
                                                break;
                                }
                        }
+
+                       /*
+                        * Refuse to use a deferrable unique/primary key.  This is per
+                        * SQL spec, and there would be a lot of interesting semantic
+                        * problems if we tried to allow it.
+                        */
+                       if (found && !indexStruct->indimmediate)
+                       {
+                               /*
+                                * Remember that we found an otherwise matching index, so
+                                * that we can generate a more appropriate error message.
+                                */
+                               found_deferrable = true;
+                               found = false;
+                       }
                }
                ReleaseSysCache(indexTuple);
                if (found)
@@ -5205,10 +5220,18 @@ transformFkeyCheckAttrs(Relation pkrel,
        }
 
        if (!found)
-               ereport(ERROR,
-                               (errcode(ERRCODE_INVALID_FOREIGN_KEY),
-                                errmsg("there is no unique constraint matching given keys for referenced table \"%s\"",
-                                               RelationGetRelationName(pkrel))));
+       {
+               if (found_deferrable)
+                       ereport(ERROR,
+                                       (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+                                        errmsg("cannot use a deferrable unique constraint for referenced table \"%s\"",
+                                                       RelationGetRelationName(pkrel))));
+               else
+                       ereport(ERROR,
+                                       (errcode(ERRCODE_INVALID_FOREIGN_KEY),
+                                        errmsg("there is no unique constraint matching given keys for referenced table \"%s\"",
+                                                       RelationGetRelationName(pkrel))));
+       }
 
        list_free(indexoidlist);