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.兩個參數都是字符串，會按照字符串來比較，不做類型轉換。If both arguments are integers, they are compared as integers.兩個參數都是整數，按照整數來比較，不做類型轉換。Hexadecimal values are treated as binary strings if not compared to a number.十六進制的值和非數字做比較時，會被當做二進制串。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.有一個參數是 TIMESTAMP 或 DATETIME，并且另外一個參數是常量，常量會被轉換為 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.有一個參數是 decimal 類型，如果另外一個參數是 decimal 或者整數，會將整數轉換為 decimal 后進行比較，如果另外一個參數是浮點數，則會把 decimal 轉換為浮點數進行比較In all other cases, the arguments are compared as floating-point (real) numbers.所有其他情況下，兩個參數都會被轉換為浮點數再進行比較 

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)