diff options
Diffstat (limited to 'src/backend/executor/nodeLimit.c')
| -rw-r--r-- | src/backend/executor/nodeLimit.c | 41 |
1 files changed, 28 insertions, 13 deletions
diff --git a/src/backend/executor/nodeLimit.c b/src/backend/executor/nodeLimit.c index 4b1145e258c..7477bd43042 100644 --- a/src/backend/executor/nodeLimit.c +++ b/src/backend/executor/nodeLimit.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/executor/nodeLimit.c,v 1.15 2003/07/21 17:05:09 tgl Exp $ + * $Header: /cvsroot/pgsql/src/backend/executor/nodeLimit.c,v 1.16 2003/08/04 00:43:18 momjian Exp $ * *------------------------------------------------------------------------- */ @@ -55,17 +55,21 @@ ExecLimit(LimitState *node) switch (node->lstate) { case LIMIT_INITIAL: + /* * If backwards scan, just return NULL without changing state. */ if (!ScanDirectionIsForward(direction)) return NULL; + /* - * First call for this scan, so compute limit/offset. (We can't do - * this any earlier, because parameters from upper nodes may not - * be set until now.) This also sets position = 0. + * First call for this scan, so compute limit/offset. (We + * can't do this any earlier, because parameters from upper + * nodes may not be set until now.) This also sets position = + * 0. */ recompute_limits(node); + /* * Check for empty window; if so, treat like empty subplan. */ @@ -74,6 +78,7 @@ ExecLimit(LimitState *node) node->lstate = LIMIT_EMPTY; return NULL; } + /* * Fetch rows from subplan until we reach position > offset. */ @@ -83,8 +88,8 @@ ExecLimit(LimitState *node) if (TupIsNull(slot)) { /* - * The subplan returns too few tuples for us to produce - * any output at all. + * The subplan returns too few tuples for us to + * produce any output at all. */ node->lstate = LIMIT_EMPTY; return NULL; @@ -93,6 +98,7 @@ ExecLimit(LimitState *node) if (++node->position > node->offset) break; } + /* * Okay, we have the first tuple of the window. */ @@ -100,9 +106,10 @@ ExecLimit(LimitState *node) break; case LIMIT_EMPTY: + /* * The subplan is known to return no tuples (or not more than - * OFFSET tuples, in general). So we return no tuples. + * OFFSET tuples, in general). So we return no tuples. */ return NULL; @@ -113,7 +120,8 @@ ExecLimit(LimitState *node) * Forwards scan, so check for stepping off end of window. * If we are at the end of the window, return NULL without * advancing the subplan or the position variable; but - * change the state machine state to record having done so. + * change the state machine state to record having done + * so. */ if (!node->noCount && node->position >= node->offset + node->count) @@ -121,6 +129,7 @@ ExecLimit(LimitState *node) node->lstate = LIMIT_WINDOWEND; return NULL; } + /* * Get next tuple from subplan, if any. */ @@ -136,14 +145,16 @@ ExecLimit(LimitState *node) else { /* - * Backwards scan, so check for stepping off start of window. - * As above, change only state-machine status if so. + * Backwards scan, so check for stepping off start of + * window. As above, change only state-machine status if + * so. */ if (node->position <= node->offset + 1) { node->lstate = LIMIT_WINDOWSTART; return NULL; } + /* * Get previous tuple from subplan; there should be one! */ @@ -158,9 +169,11 @@ ExecLimit(LimitState *node) case LIMIT_SUBPLANEOF: if (ScanDirectionIsForward(direction)) return NULL; + /* * Backing up from subplan EOF, so re-fetch previous tuple; - * there should be one! Note previous tuple must be in window. + * there should be one! Note previous tuple must be in + * window. */ slot = ExecProcNode(outerPlan); if (TupIsNull(slot)) @@ -173,9 +186,10 @@ ExecLimit(LimitState *node) case LIMIT_WINDOWEND: if (ScanDirectionIsForward(direction)) return NULL; + /* - * Backing up from window end: simply re-return the last - * tuple fetched from the subplan. + * Backing up from window end: simply re-return the last tuple + * fetched from the subplan. */ slot = node->subSlot; node->lstate = LIMIT_INWINDOW; @@ -185,6 +199,7 @@ ExecLimit(LimitState *node) case LIMIT_WINDOWSTART: if (!ScanDirectionIsForward(direction)) return NULL; + /* * Advancing after having backed off window start: simply * re-return the last tuple fetched from the subplan. |