Add some code to EXPLAIN to show the targetlist (ie, output columns)

of each plan node.  For the moment this is debug support only and is
not enabled unless EXPLAIN_PRINT_TLISTS is defined at build time.
Later I'll see about the idea of letting EXPLAIN VERBOSE do it.

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index d1511b2..768ae77 100644 (file)
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994-5, Regents of the University of California
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.171 2008/03/26 18:48:59 alvherre Exp $
+ *       $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.172 2008/04/17 18:30:18 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -61,6 +61,8 @@ static void explain_outNode(StringInfo str,
                                Plan *plan, PlanState *planstate,
                                Plan *outer_plan,
                                int indent, ExplainState *es);
+static void show_plan_tlist(Plan *plan,
+                                                       StringInfo str, int indent, ExplainState *es);
 static void show_scan_qual(List *qual, const char *qlabel,
                           int scanrelid, Plan *outer_plan, Plan *inner_plan,
                           StringInfo str, int indent, ExplainState *es);
@@ -443,7 +445,7 @@ explain_outNode(StringInfo str,
                                Plan *outer_plan,
                                int indent, ExplainState *es)
 {
-       char       *pname;
+       const char *pname;
        int                     i;
 
        if (plan == NULL)
@@ -744,6 +746,9 @@ explain_outNode(StringInfo str,
                appendStringInfo(str, " (never executed)");
        appendStringInfoChar(str, '\n');
 
+       /* target list */
+       show_plan_tlist(plan, str, indent, es);
+
        /* quals, sort keys, etc */
        switch (nodeTag(plan))
        {
@@ -1044,6 +1049,56 @@ explain_outNode(StringInfo str,
 }
 
 /*
+ * Show the targetlist of a plan node
+ */
+static void
+show_plan_tlist(Plan *plan,
+                               StringInfo str, int indent, ExplainState *es)
+{
+#ifdef EXPLAIN_PRINT_TLISTS
+       List       *context;
+       bool            useprefix;
+       ListCell   *lc;
+       int                     i;
+
+       /* No work if empty tlist (this occurs eg in bitmap indexscans) */
+       if (plan->targetlist == NIL)
+               return;
+       /* The tlist of an Append isn't real helpful, so suppress it */
+       if (IsA(plan, Append))
+               return;
+
+       /* Set up deparsing context */
+       context = deparse_context_for_plan((Node *) outerPlan(plan),
+                                                                          (Node *) innerPlan(plan),
+                                                                          es->rtable);
+       useprefix = list_length(es->rtable) > 1;
+
+       /* Emit line prefix */
+       for (i = 0; i < indent; i++)
+               appendStringInfo(str, "  ");
+       appendStringInfo(str, "  Output: ");
+
+       /* Deparse each non-junk result column */
+       i = 0;
+       foreach(lc, plan->targetlist)
+       {
+               TargetEntry *tle = (TargetEntry *) lfirst(lc);
+
+               if (tle->resjunk)
+                       continue;
+               if (i++ > 0)
+                       appendStringInfo(str, ", ");
+               appendStringInfoString(str,
+                                                          deparse_expression((Node *) tle->expr, context,
+                                                                                                 useprefix, false));
+       }
+
+       appendStringInfoChar(str, '\n');
+#endif /* EXPLAIN_PRINT_TLISTS */
+}
+
+/*
  * Show a qualifier expression for a scan plan node
  *
  * Note: outer_plan is the referent for any OUTER vars in the scan qual;