Further fixes for CREATE TABLE LIKE: cope with self-referential FKs.

tglsfdc · tglsfdc · commit 6631d5f261e9 · 2020-11-19T15:03:17.000-05:00
Commit 5028981 was too careless about the order of execution of the additional ALTER TABLE operations generated by expandTableLikeClause. It just stuck them all at the end, which seems okay for most purposes. But it falls down in the case where LIKE is importing a primary key or unique index and the outer CREATE TABLE includes a FOREIGN KEY constraint that needs to depend on that index. Weird as that is, it used to work, so we ought to keep it working. To fix, make parse_utilcmd.c insert LIKE clauses between index-creation and FK-creation commands in the transformed list of commands, and change utility.c so that the commands generated by expandTableLikeClause are executed immediately not at the end. One could imagine scenarios where this wouldn't work either; but currently expandTableLikeClause only makes column default expressions, CHECK constraints, and indexes, and this ordering seems fine for those. Per bug #16730 from Sofoklis Papasofokli. Like the previous patch, back-patch to all supported branches. Discussion: https://postgr.es/m/16730-b902f7e6e0276b30@postgresql.org
diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c
@@ -78,6 +78,7 @@ typedef struct
 	List	   *ckconstraints;	/* CHECK constraints */
 	List	   *fkconstraints;	/* FOREIGN KEY constraints */
 	List	   *ixconstraints;	/* index-creating constraints */
+	List	   *likeclauses;	/* LIKE clauses that need post-processing */
 	List	   *blist;			/* "before list" of things to do before
 								 * creating the table */
 	List	   *alist;			/* "after list" of things to do after creating
@@ -221,6 +222,7 @@ transformCreateStmt(CreateStmt *stmt, const char *queryString)
 	cxt.ckconstraints = NIL;
 	cxt.fkconstraints = NIL;
 	cxt.ixconstraints = NIL;
+	cxt.likeclauses = NIL;
 	cxt.blist = NIL;
 	cxt.alist = NIL;
 	cxt.pkey = NULL;
@@ -285,6 +287,20 @@ transformCreateStmt(CreateStmt *stmt, const char *queryString)
 	 */
 	transformIndexConstraints(&cxt);
 
+	/*
+	 * Re-consideration of LIKE clauses should happen after creation of
+	 * indexes, but before creation of foreign keys.  This order is critical
+	 * because a LIKE clause may attempt to create a primary key.  If there's
+	 * also a pkey in the main CREATE TABLE list, creation of that will not
+	 * check for a duplicate at runtime (since index_check_primary_key()
+	 * expects that we rejected dups here).  Creation of the LIKE-generated
+	 * pkey behaves like ALTER TABLE ADD, so it will check, but obviously that
+	 * only works if it happens second.  On the other hand, we want to make
+	 * pkeys before foreign key constraints, in case the user tries to make a
+	 * self-referential FK.
+	 */
+	cxt.alist = list_concat(cxt.alist, cxt.likeclauses);
+
 	/*
 	 * Postprocess foreign-key constraints.
 	 */
@@ -695,7 +711,7 @@ transformTableConstraint(CreateStmtContext *cxt, Constraint *constraint)
  * Change the LIKE <srctable> portion of a CREATE TABLE statement into
  * column definitions that recreate the user defined column portions of
  * <srctable>.  Also, if there are any LIKE options that we can't fully
- * process at this point, add the TableLikeClause to cxt->alist, which
+ * process at this point, add the TableLikeClause to cxt->likeclauses, which
  * will cause utility.c to call expandTableLikeClause() after the new
  * table has been created.
  */
@@ -862,13 +878,13 @@ transformTableLikeClause(CreateStmtContext *cxt, TableLikeClause *table_like_cla
 	 * We cannot yet deal with CHECK constraints or indexes, since we don't
 	 * yet know what column numbers the copied columns will have in the
 	 * finished table.  If any of those options are specified, add the LIKE
-	 * clause to cxt->alist so that expandTableLikeClause will be called after
-	 * we do know that.
+	 * clause to cxt->likeclauses so that expandTableLikeClause will be called
+	 * after we do know that.
 	 */
 	if (table_like_clause->options &
 		(CREATE_TABLE_LIKE_CONSTRAINTS |
 		 CREATE_TABLE_LIKE_INDEXES))
-		cxt->alist = lappend(cxt->alist, table_like_clause);
+		cxt->likeclauses = lappend(cxt->likeclauses, table_like_clause);
 
 	/*
 	 * Close the parent rel, but keep our AccessShareLock on it until xact
@@ -1991,7 +2007,7 @@ transformFKConstraints(CreateStmtContext *cxt,
 	 * Note: the ADD CONSTRAINT command must also execute after any index
 	 * creation commands.  Thus, this should run after
 	 * transformIndexConstraints, so that the CREATE INDEX commands are
-	 * already in cxt->alist.
+	 * already in cxt->alist.  See also the handling of cxt->likeclauses.
 	 */
 	if (!isAddConstraint)
 	{
@@ -2500,6 +2516,7 @@ transformAlterTableStmt(Oid relid, AlterTableStmt *stmt,
 	cxt.ckconstraints = NIL;
 	cxt.fkconstraints = NIL;
 	cxt.ixconstraints = NIL;
+	cxt.likeclauses = NIL;
 	cxt.blist = NIL;
 	cxt.alist = NIL;
 	cxt.pkey = NULL;
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
@@ -948,17 +948,22 @@ ProcessUtilitySlow(Node *parsetree,
 			case T_CreateForeignTableStmt:
 				{
 					List	   *stmts;
-					ListCell   *l;
 					RangeVar   *table_rv = NULL;
 
 					/* Run parse analysis ... */
 					stmts = transformCreateStmt((CreateStmt *) parsetree,
 												queryString);
 
-					/* ... and do it */
-					foreach(l, stmts)
+					/*
+					 * ... and do it.  We can't use foreach() because we may
+					 * modify the list midway through, so pick off the
+					 * elements one at a time, the hard way.
+					 */
+					while (stmts != NIL)
 					{
-						Node	   *stmt = (Node *) lfirst(l);
+						Node	   *stmt = (Node *) linitial(stmts);
+
+						stmts = list_delete_first(stmts);
 
 						if (IsA(stmt, CreateStmt))
 						{
@@ -1022,23 +1027,16 @@ ProcessUtilitySlow(Node *parsetree,
 							/*
 							 * Do delayed processing of LIKE options.  This
 							 * will result in additional sub-statements for us
-							 * to process.  We can just tack those onto the
-							 * to-do list.
+							 * to process.  Those should get done before any
+							 * remaining actions, so prepend them to "stmts".
 							 */
 							TableLikeClause *like = (TableLikeClause *) stmt;
 							List	   *morestmts;
 
 							Assert(table_rv != NULL);
 
 							morestmts = expandTableLikeClause(table_rv, like);
-							stmts = list_concat(stmts, morestmts);
-
-							/*
-							 * We don't need a CCI now, besides which the "l"
-							 * list pointer is now possibly invalid, so just
-							 * skip the CCI test below.
-							 */
-							continue;
+							stmts = list_concat(morestmts, stmts);
 						}
 						else
 						{
@@ -1056,7 +1054,7 @@ ProcessUtilitySlow(Node *parsetree,
 						}
 
 						/* Need CCI between commands */
-						if (lnext(l) != NULL)
+						if (stmts != NIL)
 							CommandCounterIncrement();
 					}
 
diff --git a/src/test/regress/expected/create_table_like.out b/src/test/regress/expected/create_table_like.out
@@ -114,6 +114,22 @@ INSERT INTO inhg (xx, yy, x) VALUES ('foo', 10, 15); -- should fail
 ERROR:  duplicate key value violates unique constraint "inhg_x_key"
 DETAIL:  Key (x)=(15) already exists.
 DROP TABLE inhg;
+DROP TABLE inhz;
+/* Use primary key imported by LIKE for self-referential FK constraint */
+CREATE TABLE inhz (x text REFERENCES inhz, LIKE inhx INCLUDING INDEXES);
+\d inhz
+    Table "public.inhz"
+ Column | Type | Modifiers 
+--------+------+-----------
+ x      | text | 
+ xx     | text | not null
+Indexes:
+    "inhz_pkey" PRIMARY KEY, btree (xx)
+Foreign-key constraints:
+    "inhz_x_fkey" FOREIGN KEY (x) REFERENCES inhz(xx)
+Referenced by:
+    TABLE "inhz" CONSTRAINT "inhz_x_fkey" FOREIGN KEY (x) REFERENCES inhz(xx)
+
 DROP TABLE inhz;
 -- including storage and comments
 CREATE TABLE ctlt1 (a text CHECK (length(a) > 2) PRIMARY KEY, b text);
diff --git a/src/test/regress/sql/create_table_like.sql b/src/test/regress/sql/create_table_like.sql
@@ -66,6 +66,11 @@ INSERT INTO inhg (xx, yy, x) VALUES ('foo', 10, 15); -- should fail
 DROP TABLE inhg;
 DROP TABLE inhz;
 
+/* Use primary key imported by LIKE for self-referential FK constraint */
+CREATE TABLE inhz (x text REFERENCES inhz, LIKE inhx INCLUDING INDEXES);
+\d inhz
+DROP TABLE inhz;
+
 -- including storage and comments
 CREATE TABLE ctlt1 (a text CHECK (length(a) > 2) PRIMARY KEY, b text);
 CREATE INDEX ctlt1_b_key ON ctlt1 (b);
