diff options
Diffstat (limited to 'sql/sql_select.cc')
| -rw-r--r-- | sql/sql_select.cc | 32 |
1 files changed, 23 insertions, 9 deletions
diff --git a/sql/sql_select.cc b/sql/sql_select.cc index 638ed229a70..df74a946b5c 100644 --- a/sql/sql_select.cc +++ b/sql/sql_select.cc @@ -6911,10 +6911,23 @@ part_of_refkey(TABLE *table,Field *field) /***************************************************************************** Test if one can use the key to resolve ORDER BY - Returns: 1 if key is ok. - 0 if key can't be used - -1 if reverse key can be used - used_key_parts is set to key parts used if length != 0 + + SYNOPSIS + test_if_order_by_key() + order Sort order + table Table to sort + idx Index to check + used_key_parts Return value for used key parts. + + + NOTES + used_key_parts is set to correct key parts used if return value != 0 + (On other cases, used_key_part may be changed) + + RETURN + 1 key is ok. + 0 Key can't be used + -1 Reverse key can be used *****************************************************************************/ static int test_if_order_by_key(ORDER *order, TABLE *table, uint idx, @@ -6943,16 +6956,17 @@ static int test_if_order_by_key(ORDER *order, TABLE *table, uint idx, DBUG_RETURN(0); /* set flag to 1 if we can use read-next on key, else to -1 */ - flag= ((order->asc == !(key_part->key_part_flag & HA_REVERSE_SORT)) ? 1 : -1); + flag= ((order->asc == !(key_part->key_part_flag & HA_REVERSE_SORT)) ? + 1 : -1); if (reverse && flag != reverse) DBUG_RETURN(0); reverse=flag; // Remember if reverse key_part++; } - uint tmp= (uint) (key_part - table->key_info[idx].key_part); - if (reverse == -1 && !(table->file->index_flags(idx,tmp-1, 1) & HA_READ_PREV)) - DBUG_RETURN(0); - *used_key_parts= tmp; + *used_key_parts= (uint) (key_part - table->key_info[idx].key_part); + if (reverse == -1 && !(table->file->index_flags(idx, *used_key_parts-1, 1) & + HA_READ_PREV)) + reverse= 0; // Index can't be used DBUG_RETURN(reverse); } |