CREATE TABLE `a` (
`L` timestamp NOT NULL DEFAULT '2000-01-01 00:00:00',
`I` varchar(32) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
`A` varchar(32) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
`S` varchar(64) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
`F` tinyint(4) DEFAULT NULL,
`V` varchar(256) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT '',
`N` varchar(64) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
KEY `IX_L` (`L`),
KEY `IX_I` (`I`),
KEY `IX_S` (`S`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `b` (
`R` timestamp NOT NULL DEFAULT '2000-01-01 00:00:00',
`V` varchar(32) DEFAULT NULL,
`U` varchar(32) DEFAULT NULL,
`C` varchar(16) DEFAULT NULL,
`S` varchar(64) DEFAULT NULL,
`I` varchar(64) DEFAULT NULL,
`E` bigint(32) DEFAULT NULL,
`ES` varchar(128) DEFAULT NULL,
KEY `IX_R` (`R`),
KEY `IX_C` (`C`),
KEY `IX_S` (`S`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

+----+-------------+-------+-------+---------------+------+---------+----------+---------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+-------+---------------+------+---------+----------+---------+-------------+
| 1 | SIMPLE | b | index | IX_S | IX_S | 195 | NULL | 1038165 | Using index |
| 1 | SIMPLE | a | ref | IX_L,IX_S | IX_S | 195 | test.b.S | 1 | Using where |
+----+-------------+-------+-------+---------------+------+---------+----------+---------+-------------+

explain SELECT count(*) FROM a straight_join b ON a.`S` = b.`S` WHERE a.`L` > '2014-03-30 00:55:00' AND a.`L` < '2014-03-30 01:00:00' ;

+----+-------------+-------+-------+---------------+------+---------+------+---------+---------------------------------------------+

| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |

+----+-------------+-------+-------+---------------+------+---------+------+---------+---------------------------------------------+

| 1 | SIMPLE | a | range | IX_L,IX_S | IX_L | 4 | NULL | 63 | Using where |

| 1 | SIMPLE | b | index | IX_S | IX_S | 195 | NULL | 1038165 | Using where; Using index; Using join buffer |

+----+-------------+-------+-------+---------------+------+---------+------+---------+---------------------------------------------+

mysql> select * from information_schema.STATISTICS where table_name='b' and index_name='IX_S'\G
*************************** 1. row ***************************
TABLE_CATALOG: def
TABLE_SCHEMA: test
TABLE_NAME: b
NON_UNIQUE: 1
INDEX_SCHEMA: test
INDEX_NAME: IX_S
SEQ_IN_INDEX: 1
COLUMN_NAME: S
COLLATION: A
CARDINALITY: 1038165
SUB_PART: NULL
PACKED: NULL
NULLABLE: YES
INDEX_TYPE: BTREE
COMMENT:
INDEX_COMMENT:

show table status like 'b'\G
*************************** 1. row ***************************
Name: b
Engine: InnoDB
Version: 10
Row_format: Compact
Rows: 1038165
Avg_row_length: 114
Data_length: 119160832
Max_data_length: 0
Index_length: 109953024
Data_free: 5242880
Auto_increment: NULL
Create_time: 2014-05-23 00:24:25
Update_time: NULL
Check_time: NULL
Collation: utf8_general_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.00 sec)

mysql> explain SELECT * FROM a straight_JOIN b ON binary a.`S` = b.`S` WHERE a.`L` > '2014-03-30 00:55:00' AND a.`L` < '2014-03-30 01:00:00' ;

+—-+————-+——-+——-+—————+——+———+——+———+————————————————+

| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |

+—-+————-+——-+——-+—————+——+———+——+———+————————————————+

| 1 | SIMPLE | a | range | IX_L | IX_L | 4 | NULL | 63 | Using where |

| 1 | SIMPLE | b | ALL | IX_S | NULL | NULL | NULL | 1038165 | Range checked for each record (index map: 0x4) |

+—-+————-+——-+——-+—————+——+———+——+———+————————————————+

1、select count(*) from b join (select s from a WHERE a.`L` > '2014-03-30 00:55:00' AND a.`L` < '2014-03-30 01:00:00') ta on b.S=ta.s;

2、SELECT count(*) FROM a JOIN b ON binary a.`S` = b.`S` WHERE a.`L` > '2014-03-30 00:55:00' AND a.`L` < '2014-03-30 01:00:00' ;