diff options
Diffstat (limited to 'src/include/nodes/primnodes.h')
| -rw-r--r-- | src/include/nodes/primnodes.h | 42 |
1 files changed, 28 insertions, 14 deletions
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h index eb2cacb3a72..d73be2ad46c 100644 --- a/src/include/nodes/primnodes.h +++ b/src/include/nodes/primnodes.h @@ -141,18 +141,32 @@ typedef struct Expr /* * Var - expression node representing a variable (ie, a table column) * - * Note: during parsing/planning, varnoold/varoattno are always just copies - * of varno/varattno. At the tail end of planning, Var nodes appearing in - * upper-level plan nodes are reassigned to point to the outputs of their - * subplans; for example, in a join node varno becomes INNER_VAR or OUTER_VAR - * and varattno becomes the index of the proper element of that subplan's - * target list. Similarly, INDEX_VAR is used to identify Vars that reference - * an index column rather than a heap column. (In ForeignScan and CustomScan - * plan nodes, INDEX_VAR is abused to signify references to columns of a - * custom scan tuple type.) In all these cases, varnoold/varoattno hold the - * original values. The code doesn't really need varnoold/varoattno, but they - * are very useful for debugging and interpreting completed plans, so we keep - * them around. + * In the parser and planner, varno and varattno identify the semantic + * referent, which is a base-relation column unless the reference is to a join + * USING column that isn't semantically equivalent to either join input column + * (because it is a FULL join or the input column requires a type coercion). + * In those cases varno and varattno refer to the JOIN RTE. (Early in the + * planner, we replace such join references by the implied expression; but up + * till then we want join reference Vars to keep their original identity for + * query-printing purposes.) + * + * At the end of planning, Var nodes appearing in upper-level plan nodes are + * reassigned to point to the outputs of their subplans; for example, in a + * join node varno becomes INNER_VAR or OUTER_VAR and varattno becomes the + * index of the proper element of that subplan's target list. Similarly, + * INDEX_VAR is used to identify Vars that reference an index column rather + * than a heap column. (In ForeignScan and CustomScan plan nodes, INDEX_VAR + * is abused to signify references to columns of a custom scan tuple type.) + * + * In the parser, varnosyn and varattnosyn are either identical to + * varno/varattno, or they specify the column's position in an aliased JOIN + * RTE that hides the semantic referent RTE's refname. This is a syntactic + * identifier as opposed to the semantic identifier; it tells ruleutils.c + * how to print the Var properly. varnosyn/varattnosyn retain their values + * throughout planning and execution, so they are particularly helpful to + * identify Vars when debugging. Note, however, that a Var that is generated + * in the planner and doesn't correspond to any simple relation column may + * have varnosyn = varattnosyn = 0. */ #define INNER_VAR 65000 /* reference to inner subplan */ #define OUTER_VAR 65001 /* reference to outer subplan */ @@ -177,8 +191,8 @@ typedef struct Var Index varlevelsup; /* for subquery variables referencing outer * relations; 0 in a normal var, >0 means N * levels up */ - Index varnoold; /* original value of varno, for debugging */ - AttrNumber varoattno; /* original value of varattno */ + Index varnosyn; /* syntactic relation index (0 if unknown) */ + AttrNumber varattnosyn; /* syntactic attribute number */ int location; /* token location, or -1 if unknown */ } Var; |