Add CTE support (#47)

Simple CTEs which does not contain aggregates or DISTINCT are 
now supported similarly to simple sub-queries.

Before a view is maintained, all CTEs are converted to corresponding
subqueries to enable to treat CTEs as same as subqueries. For this
end, codes of the static function inline_cte in the core
(optimizer/plan/subselect.c) was imported.

Prohibit Unreferenced CTE is prohibited.
When a table in a unreferenced CTE is TRUNCATEd, the contents
of the IMMV is not affected so it must not be truncated. For
confirming it at the maintenance time, we have to check if the
modified table used in a CTE is actually referenced. Although
it would possible, we just disallow to create such IMMVs for now
since such unreferenced CTE is useless unless it doesn't contain
modifying commands, that is already prohibited.

Author: yugo-n

Makefile

@@ -6,7 +6,8 @@ OBJS = \
 	createas.o \
 	matview.o \
 	pg_ivm.o \
-	ruleutils.o
+	ruleutils.o \
+	subselect.o
 PGFILEDESC = "pg_ivm - incremental view maintenance on PostgreSQL"
 
 EXTENSION = pg_ivm

README.md

@@ -188,7 +188,7 @@ Time: 3224.741 ms (00:03.225)
 
 ## Supported View Definitions and Restriction
 
-Currently, IMMV's view definition can contain inner joins, DISTINCT clause, some built-in aggregate functions, and simple sub-queries in `FROM` clause. Inner joins including self-join are supported, but outer joins are not supported. Supported aggregate functions are count, sum, avg, min and max. Other aggregates, sub-queries which contain an aggregate or `DISTINCT` clause, sub-queries in other than `FROM` clause, CTEs, window functions, `HAVING`, `ORDER BY`, `LIMIT`/`OFFSET`, `UNION`/`INTERSECT`/`EXCEPT`, `DISTINCT ON`, `TABLESAMPLE`, `VALUES`, and `FOR UPDATE`/`SHARE` can not be used in view definition.
+Currently, IMMV's view definition can contain inner joins, DISTINCT clause, some built-in aggregate functions, simple sub-queries in `FROM` clause, and simple CTE (`WITH` query). Inner joins including self-join are supported, but outer joins are not supported. Supported aggregate functions are count, sum, avg, min and max. Other aggregates, sub-queries which contain an aggregate or `DISTINCT` clause, sub-queries in other than `FROM` clause, window functions, `HAVING`, `ORDER BY`, `LIMIT`/`OFFSET`, `UNION`/`INTERSECT`/`EXCEPT`, `DISTINCT ON`, `TABLESAMPLE`, `VALUES`, and `FOR UPDATE`/`SHARE` can not be used in view definition.
 
 The base tables must be simple tables. Views, materialized views, inheritance parent tables, partitioned tables, partitions, and foreign tables can not be used.
 
@@ -224,6 +224,16 @@ Subqueries can be used only in `FROM` clause. Subqueries in target list or `WHER
 
 Subqueries containing an aggregate function or `DISTINCT` are not supported.
 
+### CTE
+
+Simple CTEs (`WITH` queries) are supported.
+
+#### Restrictions on Subqueries
+
+`WITH` queries containing an aggregate function or `DISTINCT` are not supported.
+
+Recursive queries (`WITH RECURSIVE`) are not allowed. Unreferenced CTEs are not allowed either, that is, a CTE must be referenced at least once in the view definition query.
+
 ### DISTINCT
 
 `DISTINCT` is allowed in IMMV's definition queries. Suppose an IMMV defined with DISTINCT on a base table containing duplicate tuples.  When tuples are deleted from the base table, a tuple in the view is deleted if and only if the multiplicity of the tuple becomes zero.  Moreover, when tuples are inserted into the base table, a tuple is inserted into the view only if the same tuple doesn't already exist in it.

createas.c

@@ -522,8 +522,15 @@ CreateIvmTriggersOnBaseTablesRecurse(Query *qry, Node *node, Oid matviewOid,
 		case T_Query:
 			{
 				Query *query = (Query *) node;
+				ListCell *lc;
 
 				CreateIvmTriggersOnBaseTablesRecurse(qry, (Node *)query->jointree, matviewOid, relids, ex_lock);
+				foreach(lc, query->cteList)
+				{
+					CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);
+					Assert(IsA(cte->ctequery, Query));
+					CreateIvmTriggersOnBaseTablesRecurse((Query *) cte->ctequery, cte->ctequery, matviewOid, relids, ex_lock);
+				}
 			}
 			break;
 
@@ -706,11 +713,6 @@ check_ivm_restriction_walker(Node *node, check_ivm_restriction_context *context)
 				ListCell   *lc;
 				List       *vars;
 
-				/* if contained CTE, return error */
-				if (qry->cteList != NIL)
-					ereport(ERROR,
-							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-							 errmsg("CTE is not supported on incrementally maintainable materialized view")));
 				if (qry->groupClause != NIL && !qry->hasAggs)
 					ereport(ERROR,
 							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@@ -751,6 +753,10 @@ check_ivm_restriction_walker(Node *node, check_ivm_restriction_context *context)
 					ereport(ERROR,
 							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 							 errmsg("FOR UPDATE/SHARE clause is not supported on incrementally maintainable materialized view")));
+				if (qry->hasRecursive)
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							 errmsg("recursive query is not supported on incrementally maintainable materialized view")));
 
 				/* system column restrictions */
 				vars = pull_vars_of_level((Node *) qry, 0);
@@ -835,6 +841,34 @@ check_ivm_restriction_walker(Node *node, check_ivm_restriction_context *context)
 
 				query_tree_walker(qry, check_ivm_restriction_walker, (void *) context, QTW_IGNORE_RT_SUBQUERIES);
 
+				break;
+			}
+		case T_CommonTableExpr:
+			{
+				CommonTableExpr *cte = (CommonTableExpr *) node;
+
+				if (isIvmName(cte->ctename))
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							 errmsg("WITH query name %s is not supported on incrementally maintainable materialized view", cte->ctename)));
+
+				/* 
+				 * When a table in a unreferenced CTE is TRUNCATEd, the contents of the
+				 * IMMV is not affected so it must not be truncated. For confirming it
+				 * at the maintenance time, we have to check if the modified table used
+				 * in a CTE is actually referenced. Although it would be possible, we
+				 * just disallow to create such IMMVs for now since such unreferenced
+				 * CTE is useless unless it doesn't contain modifying commands, that is
+				 * already prohibited.
+				 */
+				if (cte->cterefcount == 0)
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							 errmsg("Ureferenced WITH query is not supported on incrementally maintainable materialized view")));
+
+				context->sublevels_up++;
+				check_ivm_restriction_walker(cte->ctequery, (void *) context);
+				context->sublevels_up--;
 				break;
 			}
 		case T_TargetEntry:
@@ -1315,6 +1349,21 @@ get_primary_key_attnos_from_query(Query *query, List **constraintList, bool is_c
 	Bitmapset *keys = NULL;
 	Relids	rels_in_from;
 
+	/* convert CTEs to subqueries */
+	query = copyObject(query);
+	foreach (lc, query->cteList)
+	{
+		PlannerInfo root;
+		CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);
+
+		if (cte->cterefcount == 0)
+			continue;
+
+		root.parse = query;
+		inline_cte(&root, cte);
+	}
+	query->cteList = NIL;
+
 	/*
 	 * Collect primary key attributes from all tables used in query. The key attributes
 	 * sets for each table are stored in key_attnos_list in order by RTE index.