* pull_up_sublinks
* inline_set_returning_functions
* pull_up_subqueries
+ * flatten_simple_union_all
* do expression preprocessing (including flattening JOIN alias vars)
* reduce_outer_joins
*
List *rtable;
/*
- * Append the subquery rtable entries to upper query.
- */
- rtoffset = list_length(root->parse->rtable);
-
- /*
* Append child RTEs to parent rtable.
*
* Upper-level vars in subquery are now one level closer to their parent
* because any such vars must refer to stuff above the level of the query
* we are pulling into.
*/
+ rtoffset = list_length(root->parse->rtable);
rtable = copyObject(subquery->rtable);
IncrementVarSublevelsUp_rtable(rtable, -1, 1);
root->parse->rtable = list_concat(root->parse->rtable, rtable);
/*
* Recursively scan the subquery's setOperations tree and add
* AppendRelInfo nodes for leaf subqueries to the parent's
- * append_rel_list.
+ * append_rel_list. Also apply pull_up_subqueries to the leaf subqueries.
*/
Assert(subquery->setOperations);
pull_up_union_leaf_queries(subquery->setOperations, root, varno, subquery,
/*
* pull_up_union_leaf_queries -- recursive guts of pull_up_simple_union_all
*
- * Note that setOpQuery is the Query containing the setOp node, whose rtable
- * is where to look up the RTE if setOp is a RangeTblRef. This is *not* the
- * same as root->parse, which is the top-level Query we are pulling up into.
+ * Build an AppendRelInfo for each leaf query in the setop tree, and then
+ * apply pull_up_subqueries to the leaf query.
+ *
+ * Note that setOpQuery is the Query containing the setOp node, whose tlist
+ * contains references to all the setop output columns. When called from
+ * pull_up_simple_union_all, this is *not* the same as root->parse, which is
+ * the parent Query we are pulling up into.
*
* parentRTindex is the appendrel parent's index in root->parse->rtable.
*
- * The child RTEs have already been copied to the parent. childRToffset
- * tells us where in the parent's range table they were copied.
+ * The child RTEs have already been copied to the parent. childRToffset
+ * tells us where in the parent's range table they were copied. When called
+ * from flatten_simple_union_all, childRToffset is 0 since the child RTEs
+ * were already in root->parse->rtable and no RT index adjustment is needed.
*/
static void
pull_up_union_leaf_queries(Node *setOp, PlannerInfo *root, int parentRTindex,
return newnode;
}
+
+/*
+ * flatten_simple_union_all
+ * Try to optimize top-level UNION ALL structure into an appendrel
+ *
+ * If a query's setOperations tree consists entirely of simple UNION ALL
+ * operations, flatten it into an append relation, which we can process more
+ * intelligently than the general setops case. Otherwise, do nothing.
+ *
+ * In most cases, this can succeed only for a top-level query, because for a
+ * subquery in FROM, the parent query's invocation of pull_up_subqueries would
+ * already have flattened the UNION via pull_up_simple_union_all. But there
+ * are a few cases we can support here but not in that code path, for example
+ * when the subquery also contains ORDER BY.
+ */
+void
+flatten_simple_union_all(PlannerInfo *root)
+{
+ Query *parse = root->parse;
+ SetOperationStmt *topop;
+ Node *leftmostjtnode;
+ int leftmostRTI;
+ RangeTblEntry *leftmostRTE;
+ int childRTI;
+ RangeTblEntry *childRTE;
+ RangeTblRef *rtr;
+
+ /* Shouldn't be called unless query has setops */
+ topop = (SetOperationStmt *) parse->setOperations;
+ Assert(topop && IsA(topop, SetOperationStmt));
+
+ /* Can't optimize away a recursive UNION */
+ if (root->hasRecursion)
+ return;
+
+ /*
+ * Recursively check the tree of set operations. If not all UNION ALL
+ * with identical column types, punt.
+ */
+ if (!is_simple_union_all_recurse((Node *) topop, parse, topop->colTypes))
+ return;
+
+ /*
+ * Locate the leftmost leaf query in the setops tree. The upper query's
+ * Vars all refer to this RTE (see transformSetOperationStmt).
+ */
+ leftmostjtnode = topop->larg;
+ while (leftmostjtnode && IsA(leftmostjtnode, SetOperationStmt))
+ leftmostjtnode = ((SetOperationStmt *) leftmostjtnode)->larg;
+ Assert(leftmostjtnode && IsA(leftmostjtnode, RangeTblRef));
+ leftmostRTI = ((RangeTblRef *) leftmostjtnode)->rtindex;
+ leftmostRTE = rt_fetch(leftmostRTI, parse->rtable);
+ Assert(leftmostRTE->rtekind == RTE_SUBQUERY);
+
+ /*
+ * Make a copy of the leftmost RTE and add it to the rtable. This copy
+ * will represent the leftmost leaf query in its capacity as a member
+ * of the appendrel. The original will represent the appendrel as a
+ * whole. (We must do things this way because the upper query's Vars
+ * have to be seen as referring to the whole appendrel.)
+ */
+ childRTE = copyObject(leftmostRTE);
+ parse->rtable = lappend(parse->rtable, childRTE);
+ childRTI = list_length(parse->rtable);
+
+ /* Modify the setops tree to reference the child copy */
+ ((RangeTblRef *) leftmostjtnode)->rtindex = childRTI;
+
+ /* Modify the formerly-leftmost RTE to mark it as an appendrel parent */
+ leftmostRTE->inh = true;
+
+ /*
+ * Form a RangeTblRef for the appendrel, and insert it into FROM. The top
+ * Query of a setops tree should have had an empty FromClause initially.
+ */
+ rtr = makeNode(RangeTblRef);
+ rtr->rtindex = leftmostRTI;
+ Assert(parse->jointree->fromlist == NIL);
+ parse->jointree->fromlist = list_make1(rtr);
+
+ /*
+ * Now pretend the query has no setops. We must do this before trying
+ * to do subquery pullup, because of Assert in pull_up_simple_subquery.
+ */
+ parse->setOperations = NULL;
+
+ /*
+ * Build AppendRelInfo information, and apply pull_up_subqueries to the
+ * leaf queries of the UNION ALL. (We must do that now because they
+ * weren't previously referenced by the jointree, and so were missed by
+ * the main invocation of pull_up_subqueries.)
+ */
+ pull_up_union_leaf_queries((Node *) topop, root, leftmostRTI, parse, 0);
+}
+
+
/*
* reduce_outer_joins
* Attempt to reduce outer joins to plain inner joins.
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