diff options
Diffstat (limited to 'sql/sql_select.cc')
| -rw-r--r-- | sql/sql_select.cc | 20 |
1 files changed, 16 insertions, 4 deletions
diff --git a/sql/sql_select.cc b/sql/sql_select.cc index cb391314603..66879a39e95 100644 --- a/sql/sql_select.cc +++ b/sql/sql_select.cc @@ -2149,11 +2149,14 @@ JOIN::optimize_inner() if (sel->having != having && having_value == Item::COND_OK) thd->change_item_tree(&sel->having, having); } + bool zero_limit= !unit->lim.get_select_limit() || + (unit->lim.get_select_limit() == + unit->lim.get_offset_limit()); + if (cond_value == Item::COND_FALSE || having_value == Item::COND_FALSE || - (!unit->lim.get_select_limit() && - !(select_options & OPTION_FOUND_ROWS))) + (zero_limit && !(select_options & OPTION_FOUND_ROWS))) { /* Impossible cond */ - if (unit->lim.get_select_limit()) + if (!zero_limit) { DBUG_PRINT("info", (having_value == Item::COND_FALSE ? "Impossible HAVING" : "Impossible WHERE")); @@ -24304,7 +24307,16 @@ JOIN_TAB::remove_duplicates() field_count++; } - if (!field_count && !(join->select_options & OPTION_FOUND_ROWS) && !having) + /* + If the select list does not have any non-constant items, then all rows + are identical. Adjust the LIMIT to just produce the first row. + Exceptions to this are: + - SQL_CALC_FOUND_ROWS + - when HAVING caluse is present (we'll need to check it) + - when there's a non-zero OFFSET clause + */ + if (!field_count && !(join->select_options & OPTION_FOUND_ROWS) && !having && + !join->unit->lim.get_offset_limit()) { // only const items with no OPTION_FOUND_ROWS join->unit->lim.set_single_row(); // Only send first row DBUG_RETURN(false); |