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BUG#12915: Added single-table UPDATE/DELTE ... ORDER BY ... LIMIT

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optimization: now can use index to find records to update/delete
when there is no WHERE clause.
This commit is contained in:
sergefp@mysql.com
2005-09-30 15:21:37 +04:00
parent bd417d158e
commit e9f2f9437a
9 changed files with 343 additions and 23 deletions
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59
mysql-test/r/update.result
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@ -263,3 +263,62 @@ test
delete from t1 where count(*)=1;
ERROR HY000: Invalid use of group function
drop table t1;
create table t1 ( a int, index (a) );
insert into t1 values (0),(0),(0),(0),(0),(0),(0),(0);
flush status;
select a from t1 order by a limit 1;
a
0
show status like 'handler_read%';
Variable_name Value
Handler_read_first 1
Handler_read_key 0
Handler_read_next 0
Handler_read_prev 0
Handler_read_rnd 0
Handler_read_rnd_next 0
flush status;
update t1 set a=unix_timestamp() order by a limit 1;
show status like 'handler_read%';
Variable_name Value
Handler_read_first 1
Handler_read_key 0
Handler_read_next 0
Handler_read_prev 0
Handler_read_rnd 1
Handler_read_rnd_next 0
flush status;
delete from t1 order by a limit 1;
show status like 'handler_read%';
Variable_name Value
Handler_read_first 1
Handler_read_key 0
Handler_read_next 0
Handler_read_prev 0
Handler_read_rnd 0
Handler_read_rnd_next 0
flush status;
delete from t1 order by a desc limit 1;
show status like 'handler_read%';
Variable_name Value
Handler_read_first 0
Handler_read_key 0
Handler_read_next 0
Handler_read_prev 0
Handler_read_rnd 1
Handler_read_rnd_next 9
alter table t1 disable keys;
flush status;
delete from t1 order by a limit 1;
show status like 'handler_read%';
Variable_name Value
Handler_read_first 0
Handler_read_key 0
Handler_read_next 0
Handler_read_prev 0
Handler_read_rnd 1
Handler_read_rnd_next 9
select count(*) from t1;
count(*)
5
drop table t1;