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=utf8
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 | 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_151
Create 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=utf8
SELECT * FROM poll_joined_151 WHERE poll_id = '2348993' AND anonymous =0 ORDER BY add_time DESC LIMIT 0 , 3
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: poll_joined_151
type: ref
possible_keys: idx_poll_id_uid_add_time,idx_anonymous_id_addtime
key: idx_anonymous_id_addtime
key_len: 9
ref: const,const
rows: 30240
Extra: Using where 

If both arguments in a comparison operation are strings, they are compared as strings.
兩個參數(shù)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(shù)都是整數(shù)，按照整數(shù)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(shù)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(shù)是 TIMESTAMP 或 DATETIME，并且另外一個參數(shù)是常量，常量會被轉換為 timestamp
If 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(shù)是 decimal 類型，如果另外一個參數(shù)是 decimal 或者整數(shù)，會將整數(shù)轉換為 decimal 后進行比較，如果另外一個參數(shù)是浮點數(shù)，則會把 decimal 轉換為浮點數(shù)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(shù)都會被轉換為浮點數(shù)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)