diff options
Diffstat (limited to 'src/include/nodes/parsenodes.h')
| -rw-r--r-- | src/include/nodes/parsenodes.h | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h index 89335d95e7b..fbbbe647a43 100644 --- a/src/include/nodes/parsenodes.h +++ b/src/include/nodes/parsenodes.h @@ -1090,6 +1090,14 @@ typedef struct RangeTblEntry * alias Vars are generated only for merged columns). We keep these * entries only because they're needed in expandRTE() and similar code. * + * Vars appearing within joinaliasvars are marked with varnullingrels sets + * that describe the nulling effects of this join and lower ones. This is + * essential for FULL JOIN cases, because the COALESCE expression only + * describes the semantics correctly if its inputs have been nulled by the + * join. For other cases, it allows expandRTE() to generate a valid + * representation of the join's output without consulting additional + * parser state. + * * Within a Query loaded from a stored rule, it is possible for non-merged * joinaliasvars items to be null pointers, which are placeholders for * (necessarily unreferenced) columns dropped since the rule was made. |