diff options
Diffstat (limited to 'src/backend/tcop/pquery.c')
| -rw-r--r-- | src/backend/tcop/pquery.c | 33 |
1 files changed, 30 insertions, 3 deletions
diff --git a/src/backend/tcop/pquery.c b/src/backend/tcop/pquery.c index a3c27d9d74b..57ffd9bc4c4 100644 --- a/src/backend/tcop/pquery.c +++ b/src/backend/tcop/pquery.c @@ -1472,9 +1472,8 @@ PortalRunFetch(Portal portal, * DoPortalRunFetch * Guts of PortalRunFetch --- the portal context is already set up * - * count <= 0 is interpreted as a no-op: the destination gets started up - * and shut down, but nothing else happens. Also, count == FETCH_ALL is - * interpreted as "all rows". (cf FetchStmt.howMany) + * Here, count < 0 typically reverses the direction. Also, count == FETCH_ALL + * is interpreted as "all rows". (cf FetchStmt.howMany) * * Returns number of rows processed (suitable for use in result tag) */ @@ -1491,6 +1490,15 @@ DoPortalRunFetch(Portal portal, portal->strategy == PORTAL_ONE_MOD_WITH || portal->strategy == PORTAL_UTIL_SELECT); + /* + * Note: we disallow backwards fetch (including re-fetch of current row) + * for NO SCROLL cursors, but we interpret that very loosely: you can use + * any of the FetchDirection options, so long as the end result is to move + * forwards by at least one row. Currently it's sufficient to check for + * NO SCROLL in DoPortalRewind() and in the forward == false path in + * PortalRunSelect(); but someday we might prefer to account for that + * restriction explicitly here. + */ switch (fdirection) { case FETCH_FORWARD: @@ -1668,6 +1676,25 @@ DoPortalRewind(Portal portal) { QueryDesc *queryDesc; + /* + * No work is needed if we've not advanced nor attempted to advance the + * cursor (and we don't want to throw a NO SCROLL error in this case). + */ + if (portal->atStart && !portal->atEnd) + return; + + /* + * Otherwise, cursor should allow scrolling. However, we're only going to + * enforce that policy fully beginning in v15. In older branches, insist + * on this only if the portal has a holdStore. That prevents users from + * seeing that the holdStore may not have all the rows of the query. + */ + if ((portal->cursorOptions & CURSOR_OPT_NO_SCROLL) && portal->holdStore) + ereport(ERROR, + (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), + errmsg("cursor can only scan forward"), + errhint("Declare it with SCROLL option to enable backward scan."))); + /* Rewind holdStore, if we have one */ if (portal->holdStore) { |