Clarify old comment about qual_is_pushdown_safe's handling of subplans.

tglsfdc · tglsfdc · commit 801386af62ea · 2017-11-28T23:32:17.000-05:00
This comment glossed over the difference between initplans and subplans,
but they are indeed different for our purposes here.
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
@@ -2840,9 +2840,11 @@ targetIsInAllPartitionLists(TargetEntry *tle, Query *query)
  *
  * Conditions checked here:
  *
- * 1. The qual must not contain any subselects (mainly because I'm not sure
- * it will work correctly: sublinks will already have been transformed into
- * subplans in the qual, but not in the subquery).
+ * 1. The qual must not contain any SubPlans (mainly because I'm not sure
+ * it will work correctly: SubLinks will already have been transformed into
+ * SubPlans in the qual, but not in the subquery).  Note that SubLinks that
+ * transform to initplans are safe, and will be accepted here because what
+ * we'll see in the qual is just a Param referencing the initplan output.
  *
  * 2. If unsafeVolatile is set, the qual must not contain any volatile
  * functions.

Original file line number	Diff line number	Diff line change
`@@ -2840,9 +2840,11 @@ targetIsInAllPartitionLists(TargetEntry tle, Query query)`
`2840`	`2840`	`*`
`2841`	`2841`	`* Conditions checked here:`
`2842`	`2842`	`*`
`2843`		`- * 1. The qual must not contain any subselects (mainly because I'm not sure`
`2844`		`- * it will work correctly: sublinks will already have been transformed into`
`2845`		`- * subplans in the qual, but not in the subquery).`
	`2843`	`+ * 1. The qual must not contain any SubPlans (mainly because I'm not sure`
	`2844`	`+ * it will work correctly: SubLinks will already have been transformed into`
	`2845`	`+ * SubPlans in the qual, but not in the subquery). Note that SubLinks that`
	`2846`	`+ * transform to initplans are safe, and will be accepted here because what`
	`2847`	`+ * we'll see in the qual is just a Param referencing the initplan output.`
`2846`	`2848`	`*`
`2847`	`2849`	`* 2. If unsafeVolatile is set, the qual must not contain any volatile`
`2848`	`2850`	`* functions.`