diff options
Diffstat (limited to 'src/include/nodes/parsenodes.h')
| -rw-r--r-- | src/include/nodes/parsenodes.h | 22 |
1 files changed, 14 insertions, 8 deletions
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h index 9415e2c636e..b4013e893dc 100644 --- a/src/include/nodes/parsenodes.h +++ b/src/include/nodes/parsenodes.h @@ -660,7 +660,7 @@ typedef struct XmlSerialize * a stored rule might contain entries for columns dropped since the rule * was created. (This is only possible for columns not actually referenced * in the rule.) When loading a stored rule, we replace the joinaliasvars - * items for any such columns with NULL Consts. (We can't simply delete + * items for any such columns with null pointers. (We can't simply delete * them from the joinaliasvars list, because that would affect the attnums * of Vars referencing the rest of the list.) * @@ -731,13 +731,19 @@ typedef struct RangeTblEntry /* * Fields valid for a join RTE (else NULL/zero): * - * joinaliasvars is a list of Vars or COALESCE expressions corresponding - * to the columns of the join result. An alias Var referencing column K - * of the join result can be replaced by the K'th element of joinaliasvars - * --- but to simplify the task of reverse-listing aliases correctly, we - * do not do that until planning time. In a Query loaded from a stored - * rule, it is also possible for joinaliasvars items to be NULL Consts, - * denoting columns dropped since the rule was made. + * joinaliasvars is a list of (usually) Vars corresponding to the columns + * of the join result. An alias Var referencing column K of the join + * result can be replaced by the K'th element of joinaliasvars --- but to + * simplify the task of reverse-listing aliases correctly, we do not do + * that until planning time. In detail: an element of joinaliasvars can + * be a Var of one of the join's input relations, or such a Var with an + * implicit coercion to the join's output column type, or a COALESCE + * expression containing the two input column Vars (possibly coerced). + * Within a Query loaded from a stored rule, it is also possible for + * joinaliasvars items to be null pointers, which are placeholders for + * (necessarily unreferenced) columns dropped since the rule was made. + * Also, once planning begins, joinaliasvars items can be almost anything, + * as a result of subquery-flattening substitutions. */ JoinType jointype; /* type of join */ List *joinaliasvars; /* list of alias-var expansions */ |