diff options
| -rw-r--r-- | src/backend/executor/execExpr.c | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/src/backend/executor/execExpr.c b/src/backend/executor/execExpr.c index d1c2bbbd44a..5267a011bbb 100644 --- a/src/backend/executor/execExpr.c +++ b/src/backend/executor/execExpr.c @@ -1116,6 +1116,18 @@ ExecInitExprRec(Expr *node, PlanState *parent, ExprState *state, * field assignment can't be within a CASE either. (So * saving and restoring innermost_caseval is just * paranoia, but let's do it anyway.) + * + * Another non-obvious point is that it's safe to use the + * field's values[]/nulls[] entries as both the caseval + * source and the result address for this subexpression. + * That's okay only because (1) both FieldStore and + * ArrayRef evaluate their arg or refexpr inputs first, + * and (2) any such CaseTestExpr is directly the arg or + * refexpr input. So any read of the caseval will occur + * before there's a chance to overwrite it. Also, if + * multiple entries in the newvals/fieldnums lists target + * the same field, they'll effectively be applied + * left-to-right which is what we want. */ save_innermost_caseval = state->innermost_caseval; save_innermost_casenull = state->innermost_casenull; |