[MySQL优化案例]系列 -- 用TIMESTAMP类型取代INT和DATETIME
作/译者：叶金荣（Email: 
），来源：http://imysql.cn，转载请注明作/译者和出处，并且不能用于商业用途，违者必究。
），来源：http://imysql.cn，转载请注明作/译者和出处，并且不能用于商业用途，违者必究。
引言：在以前，我总是习惯用 INT UNSIGNED 来存储一个转换成Unix时间戳的时间值，认为这样做从索引，比较等角度来讲，都会比较高效。现在我们来对比下 TIMESTAMP 和 INT UNSIGNED 以及 DATETIME 这3种类型到底谁更好。
1. 准备
创建一个测试表：
mysql> CREATE TABLE `t` ( `d1` int(10) unsigned NOT NULL default '0', `d2` timestamp NOT NULL default CURRENT_TIMESTAMP, `d3` datetime NOT NULL, KEY `d2` (`d2`), KEY `d1` (`d1`), KEY `d3` (`d3`) );
然后创建一个存储过程填充数据：
mysql> DELIMITER // CREATE PROCEDURE INS_T() BEGIN SET @i=1; WHILE 0<1 DO SET @i=@i+1; INSERT INTO i VALUES (1199116800+@i, FROM_UNIXTIME(1199116800+@i), FROM_UNIXTIME(1199116800+@i)); END WHILE; END;// DELIMITER ;
时间戳
1199116800 表示
2008-01-01 这个时间点。然后运行存储过程，大概填充几十万条记录后，中止执行，因为上面的存储过程是个死循环，所以需要人工中止。
来看看到底有多少条记录了，以及索引情况：
来看看到底有多少条记录了，以及索引情况：
mysql> select count(*) from t; +----------+ | count(*) | +----------+ | 924707 | +----------+ mysql> analyze table t; +--------+---------+----------+-----------------------------+ | Table | Op | Msg_type | Msg_text | +--------+---------+----------+-----------------------------+ | test.t | analyze | status | Table is already up to date | +--------+---------+----------+-----------------------------+ mysql> show index from t; +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | t | 1 | d2 | 1 | d2 | A | 924707 | NULL | NULL | | BTREE | | | t | 1 | d1 | 1 | d1 | A | 924707 | NULL | NULL | | BTREE | | | t | 1 | d3 | 1 | d3 | A | 924707 | NULL | NULL | | BTREE | | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
2. 对比
2.1 只检索一条记录
mysql> explain select * from t where d1 = 1199579155; +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ | 1 | SIMPLE | t | ref | d1 | d1 | 4 | const | 1 | | +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ mysql> explain select * from t where d2 = '2008-01-06 08:25:55'; +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ | 1 | SIMPLE | t | ref | d2 | d2 | 4 | const | 1 | | +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ mysql> explain select * from t where d3 = '2008-01-06 08:25:55'; +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ | 1 | SIMPLE | t | ref | d3 | d3 | 8 | const | 1 | | +----+-------------+-------+------+---------------+------+---------+-------+------+-------+
2.2 范围检索
mysql> explain select * from t where d1 >= 1199894400; +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ | 1 | SIMPLE | t | range | d1 | d1 | 4 | NULL | 121961 | Using where | +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ mysql> explain select * from t where d2 >= from_unixtime(1199894400); +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ | 1 | SIMPLE | t | range | d2 | d2 | 4 | NULL | 121961 | Using where | +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ mysql> explain select * from t where d3 >= from_unixtime(1199894400); +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ | 1 | SIMPLE | t | range | d3 | d3 | 8 | NULL | 120625 | Using where | +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+
小结：从上面的2次对比中可以看到，对
d1 或
d2 字段检索时的索引长度都是
4，因为
TIMESTAMP 实际上是
4字节 的
INT 值。因此，实际应用中，基本上完全可以采用
TIMESTAMP 来代替另外2种类型了，并且
TIMESTAMP 还能支持自动更新成当前最新时间，何乐而不为呢？
作/译者：叶金荣（Email: ），来源：http://imysql.cn，转载请注明作/译者和出处，并且不能用于商业用途，违者必究。
），来源：http://imysql.cn，转载请注明作/译者和出处，并且不能用于商业用途，违者必究。
引言：在以前，我总是习惯用 INT UNSIGNED 来存储一个转换成Unix时间戳的时间值，认为这样做从索引，比较等角度来讲，都会比较高效。现在我们来对比下 TIMESTAMP 和 INT UNSIGNED 以及 DATETIME 这3种类型到底谁更好。
1. 准备
创建一个测试表：
mysql> CREATE TABLE `t` ( `d1` int(10) unsigned NOT NULL default '0', `d2` timestamp NOT NULL default CURRENT_TIMESTAMP, `d3` datetime NOT NULL, KEY `d2` (`d2`), KEY `d1` (`d1`), KEY `d3` (`d3`) );
然后创建一个存储过程填充数据：
mysql> DELIMITER // CREATE PROCEDURE INS_T() BEGIN SET @i=1; WHILE 0<1 DO SET @i=@i+1; INSERT INTO i VALUES (1199116800+@i, FROM_UNIXTIME(1199116800+@i), FROM_UNIXTIME(1199116800+@i)); END WHILE; END;// DELIMITER ;
时间戳
1199116800 表示
2008-01-01 这个时间点。然后运行存储过程，大概填充几十万条记录后，中止执行，因为上面的存储过程是个死循环，所以需要人工中止。
来看看到底有多少条记录了，以及索引情况：
来看看到底有多少条记录了，以及索引情况：
mysql> select count(*) from t; +----------+ | count(*) | +----------+ | 924707 | +----------+ mysql> analyze table t; +--------+---------+----------+-----------------------------+ | Table | Op | Msg_type | Msg_text | +--------+---------+----------+-----------------------------+ | test.t | analyze | status | Table is already up to date | +--------+---------+----------+-----------------------------+ mysql> show index from t; +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | t | 1 | d2 | 1 | d2 | A | 924707 | NULL | NULL | | BTREE | | | t | 1 | d1 | 1 | d1 | A | 924707 | NULL | NULL | | BTREE | | | t | 1 | d3 | 1 | d3 | A | 924707 | NULL | NULL | | BTREE | | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
2. 对比
2.1 只检索一条记录
mysql> explain select * from t where d1 = 1199579155; +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ | 1 | SIMPLE | t | ref | d1 | d1 | 4 | const | 1 | | +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ mysql> explain select * from t where d2 = '2008-01-06 08:25:55'; +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ | 1 | SIMPLE | t | ref | d2 | d2 | 4 | const | 1 | | +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ mysql> explain select * from t where d3 = '2008-01-06 08:25:55'; +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+-------+------+-------+ | 1 | SIMPLE | t | ref | d3 | d3 | 8 | const | 1 | | +----+-------------+-------+------+---------------+------+---------+-------+------+-------+
2.2 范围检索
mysql> explain select * from t where d1 >= 1199894400; +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ | 1 | SIMPLE | t | range | d1 | d1 | 4 | NULL | 121961 | Using where | +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ mysql> explain select * from t where d2 >= from_unixtime(1199894400); +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ | 1 | SIMPLE | t | range | d2 | d2 | 4 | NULL | 121961 | Using where | +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ mysql> explain select * from t where d3 >= from_unixtime(1199894400); +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+ | 1 | SIMPLE | t | range | d3 | d3 | 8 | NULL | 120625 | Using where | +----+-------------+-------+-------+---------------+------+---------+------+--------+-------------+
小结：从上面的2次对比中可以看到，对
d1 或
d2 字段检索时的索引长度都是
4，因为
TIMESTAMP 实际上是
4字节 的
INT 值。因此，实际应用中，基本上完全可以采用
TIMESTAMP 来代替另外2种类型了，并且
TIMESTAMP 还能支持自动更新成当前最新时间，何乐而不为呢？
本文出自 “MySQL中文网”博客 http://www.imysql.cn/
本文出自 “爱MySQL” 博客，转载请与作者联系！