diff options
Diffstat (limited to 'src/include/nodes/primnodes.h')
| -rw-r--r-- | src/include/nodes/primnodes.h | 32 |
1 files changed, 29 insertions, 3 deletions
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h index 10e51e40268..e2ef42218fc 100644 --- a/src/include/nodes/primnodes.h +++ b/src/include/nodes/primnodes.h @@ -6,7 +6,7 @@ * * Copyright (c) 1994, Regents of the University of California * - * $Id: primnodes.h,v 1.35 1999/08/22 20:15:00 tgl Exp $ + * $Id: primnodes.h,v 1.36 1999/08/25 23:21:36 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -319,10 +319,36 @@ typedef struct Aggref /* ---------------- * SubLink * subLinkType - EXISTS, ALL, ANY, EXPR - * useor - TRUE for <> - * lefthand - list of Var/Const nodes on the left + * useor - TRUE for <> (combine op results with "or" not "and") + * lefthand - list of outer-query expressions on the left * oper - list of Oper nodes * subselect - subselect as Query* or parsetree + * + * NOTE: lefthand and oper have varying meanings depending on where you look + * in the parse/plan pipeline: + * 1. gram.y delivers a list of the (untransformed) lefthand expressions in + * lefthand, and sets oper to a one-element list containing the string + * name of the operator. + * 2. The parser's expression transformation transforms lefthand normally, + * and replaces oper with a list of Oper nodes, one per lefthand + * expression. These nodes represent the parser's resolution of exactly + * which operator to apply to each pair of lefthand and targetlist + * expressions. However, we have not constructed actual Expr trees for + * these operators yet. This is the representation seen in saved rules + * and in the rewriter. + * 3. Finally, the planner converts the oper list to a list of normal Expr + * nodes representing the application of the operator(s) to the lefthand + * expressions and values from the inner targetlist. The inner + * targetlist items are represented by placeholder Param or Const nodes. + * The lefthand field is set to NIL, since its expressions are now in + * the Expr list. This representation is passed to the executor. + * + * Planner routines that might see either representation 2 or 3 can tell + * the difference by checking whether lefthand is NIL or not. Also, + * representation 2 appears in a "bare" SubLink, while representation 3 is + * found in SubLinks that are children of SubPlan nodes. + * + * In an EXISTS SubLink, both lefthand and oper are unused and are always NIL. * ---------------- */ typedef enum SubLinkType |