mysql TABLE_ROWS 和 count 不相等 解决办法 mysql_num_rows作用,索引的作用就是快速找出在一个列上用一特定值的行。如果没有索引,MySQL不得不首先以第一条记录开始并然后读完整个表直到它找出相关的行。索引的类型:先写一个建表语句:CREATETABLE`t_order`( `id`in
log-slow-queries=/var/lib/mysql/slowquery.log (指定日志文件存放位置,可以为空,系统会给一个缺省的文件host_name-slow.log) long_query_time=2 (记录超过的时间,默认为10s) log-queries-not-using-indexes (log下来没有使用索引的query,可以根据情况决定是否开启) log-long-format (如果设置了,所有没有使用...
在使用 MySQL 数据库时,有时候会发现使用INFORMATION_SCHEMA.TABLES查看表的行数 (TABLE_ROWS) 时与直接使用SELECT COUNT(*) FROM table_name统计的行数不一致。这可能是由于数据库统计信息不准确造成的,需要重新计算行数来解决这个问题。 解决流程 首先我们来看一下解决这个问题的步骤: 接下来我们将逐步展示每一步...
mysql> CREATE LOGFILE GROUP lg1 ADD UNDOFILE 'undofile.dat' INITIAL_SIZE = 16M UNDO_BUFFER_SIZE = 1M ENGINE = NDB; You can now see this NULL row when you query the FILES table: mysql> SELECT DISTINCT FILE_NAME AS File, FREE_EXTENTS AS Free, TOTAL_EXTENTS AS Total, EXTENT_SIZE AS...
mysql> drop index user_key on rule_ceshi.operation_log; Query OK, 0 rows affected (0.19 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> select count(*) from rule_ceshi.operation_log; +---+ | count(*) | +---+ | 21049180 | +---+ row in set (23.39 sec) 上面的测试结果表明...
Table QueryPosted by: nick clarke Date: November 18, 2009 02:22PM Hi, I a trying to work out how to do the following. I have a table with the columns runs and howout.what i want to do is work out the average. the problem is i am doing a count() on a howout but in ...
mysql> CREATE TABLE t2 (c1 VARCHAR(65533) NOT NULL) ENGINE = InnoDB CHARACTER SET latin1; Query OK, 0 rows affected (0.01 sec) For MyISAM tables, NULL columns require additional space in the row to record whether their values are NULL. Each NULL column takes one bit extra, rounded up...
mysql>setoptimizer_switch="derived_merge=off,derived_condition_pushdown=on";QueryOK,0rowsaffected(0.00sec) select_type列出现DERIVED 类型, 说明派生表没有合并,派生表会物化为临时表,但此时外查询块中的条件推入到了派生表中,相当于执行语句select * from (select id,c1 from t1 where id=2) dt,对过滤...
RENAME [TO] table_name表重命名。 RENAME {INDEX | KEY}重命名索引或键。 DROP [TABLEGROUP]删除表组。 DROP [FOREIGN KEY]删除外键。 [SET] table_option设置表级属性,可选以下参数: PRIMARY_ZONE:设置表的 Primary Zone。 REPLICA_NUM:设置表的副本数(暂不支持)。
-rw-r--- 1 mysql mysql 1024 Sep 2 10:37 m_test.MYI mysql> select count(*) from m_test; +---+ | count(*) | +---+ | 50331648 | +---+ 1 row in set (0.00 sec) mysql> select count(*) from i_test; +---+ | count(*) | +---+ | 50331648 | +---+ 1 row in ...