CREATE TABLE `appstat_day_prototype_201305` (`day_key` date NOT NULL DEFAULT '1900-01-01',`appkey` varchar(20) NOT NULL DEFAULT '',`user_total` bigint(20) NOT NULL DEFAULT '0',`user_activity` bigint(20) NOT NULL DEFAULT '0',`times_total` bigint(20) NOT NULL DEFAULT '0',`times_activity` bigint(20) NOT NULL DEFAULT '0',`incr_login_daily` bigint(20) NOT NULL DEFAULT '0',`unbind_total` bigint(20) NOT NULL DEFAULT '0',`unbind_activitys` bigint(20) NOT NULL DEFAULT '0',PRIMARY KEY (`appkey`,`day_key`)) ENGINE=InnoDB DEFAULT CHARSET=utf8mysql> explain SELECT * from appstat_day_prototype_201305 where appkey = xxxxx and day_key between '2013-05-23' and '2013-05-30';+----+-------------+------------------------------+------+---------------+------+---------+------+----------+-------------+| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |+----+-------------+------------------------------+------+---------------+------+---------+------+----------+-------------+| 1 | SIMPLE | appstat_day_prototype_201305 | ALL | PRIMARY | NULL | NULL | NULL | 19285787 | Using where |+----+-------------+------------------------------+------+---------------+------+---------+------+----------+-------------+1 row in set (0.00 sec)mysql> explain SELECT * from appstat_day_prototype_201305 where appkey = 'xxxxx' and day_key between '2013-05-23' and '2013-05-30';+----+-------------+------------------------------+-------+---------------+---------+---------+------+------+-------------+| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |+----+-------------+------------------------------+-------+---------------+---------+---------+------+------+-------------+| 1 | SIMPLE | appstat_day_prototype_201305 | range | PRIMARY | PRIMARY | 65 | NULL | 1 | Using where |+----+-------------+------------------------------+-------+---------------+---------+---------+------+------+-------------+1 row in set (0.00 sec) 

*************************** 1. row ***************************Table: poll_joined_151Create Table: CREATE TABLE `poll_joined_151` (`poll_id` bigint(11) NOT NULL,`uid` bigint(11) NOT NULL,`item_id` varchar(60) NOT NULL,`add_time` int(11) NOT NULL DEFAULT '0',`anonymous` tinyint(1) NOT NULL DEFAULT '0',`sub_item` varchar(1200) NOT NULL DEFAULT '',KEY `idx_poll_id_uid_add_time` (`poll_id`,`uid`,`add_time`),KEY `idx_anonymous_id_addtime` (`anonymous`,`poll_id`,`add_time`)) ENGINE=InnoDB DEFAULT CHARSET=utf8SELECT * FROM poll_joined_151 WHERE poll_id = '2348993' AND anonymous =0 ORDER BY add_time DESC LIMIT 0 , 3*************************** 1. row ***************************id: 1select_type: SIMPLEtable: poll_joined_151type: refpossible_keys: idx_poll_id_uid_add_time,idx_anonymous_id_addtimekey: idx_anonymous_id_addtimekey_len: 9ref: const,constrows: 30240Extra: Using where 

If both arguments in a comparison operation are strings, they are compared as strings.兩個(gè)參數(shù)都是字符串，會(huì)按照字符串來(lái)比較，不做類(lèi)型轉(zhuǎn)換。If both arguments are integers, they are compared as integers.兩個(gè)參數(shù)都是整數(shù)，按照整數(shù)來(lái)比較，不做類(lèi)型轉(zhuǎn)換。Hexadecimal values are treated as binary strings if not compared to a number.十六進(jìn)制的值和非數(shù)字做比較時(shí)，會(huì)被當(dāng)做二進(jìn)制串。If one of the arguments is a TIMESTAMP or DATETIME column and the other argument is a constant, the constant is converted to a timestamp before the comparison is performed. This is done to be more ODBC-friendly. Note that this is not done for the arguments to IN()! To be safe, always use complete datetime, date, or time strings when doing comparisons. For example, to achieve best results when using BETWEEN with date or time values, use CAST() to explicitly convert the values to the desired data type.有一個(gè)參數(shù)是 TIMESTAMP 或 DATETIME，并且另外一個(gè)參數(shù)是常量，常量會(huì)被轉(zhuǎn)換為 timestampIf one of the arguments is a decimal value, comparison depends on the other argument. The arguments are compared as decimal values if the other argument is a decimal or integer value, or as floating-point values if the other argument is a floating-point value.有一個(gè)參數(shù)是 decimal 類(lèi)型，如果另外一個(gè)參數(shù)是 decimal 或者整數(shù)，會(huì)將整數(shù)轉(zhuǎn)換為 decimal 后進(jìn)行比較，如果另外一個(gè)參數(shù)是浮點(diǎn)數(shù)，則會(huì)把 decimal 轉(zhuǎn)換為浮點(diǎn)數(shù)進(jìn)行比較In all other cases, the arguments are compared as floating-point (real) numbers.所有其他情況下，兩個(gè)參數(shù)都會(huì)被轉(zhuǎn)換為浮點(diǎn)數(shù)再進(jìn)行比較 

mysql> SELECT CAST(' 1' AS SIGNED)=1;+-------------------------+| CAST(' 1' AS SIGNED)=1 |+-------------------------+| 1 |+-------------------------+1 row in set (0.00 sec)mysql> SELECT CAST(' 1a' AS SIGNED)=1;+--------------------------+| CAST(' 1a' AS SIGNED)=1 |+--------------------------+| 1 |+--------------------------+1 row in set, 1 warning (0.00 sec)mysql> SELECT CAST('1' AS SIGNED)=1;+-----------------------+| CAST('1' AS SIGNED)=1 |+-----------------------+| 1 |+-----------------------+1 row in set (0.00 sec) 

mysql> select CAST( '30' as SIGNED) = 30;+----------------------------+| CAST( '30' as SIGNED) = 30 |+----------------------------+| 1 |+----------------------------+1 row in set (0.00 sec)