mysql联合索引与单列索引_MySQL联合索引VS单列索引
MySQL联合索引VS单列索引
以一个一千万数据量的表格为例
1. 建表建索引
USE foo;
DROP TABLE IF EXISTS tmp;
CREATE TABLE tmp (
id INT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
school_id INT UNSIGNED NOT NULL,
student_id INT UNSIGNED NOT NULL,
INDEX school_id(school_id),
INDEX student_id(student_id),
INDEX school_id_and_student_id(school_id, student_id)
);
2. 插入1000万条数据
DROP PROCEDURE IF EXISTS tmpproc;
CREATE PROCEDURE tmpproc() BEGIN
DECLARE i INT UNSIGNED DEFAULT 0;
DECLARE j INT UNSIGNED DEFAULT 0;
WHILE i < 100000 DO
SET i = i + 1;
SET j = 0;
START TRANSACTION;
WHILE j < 100 DO
INSERT INTO tmp (school_id, student_id) VALUES (i, i * 100 + j);
SET j = j + 1;
END WHILE;
COMMIT;
END WHILE;
END;
CALL tmpproc();
3. 查询速度比较
走联合索引
SELECT *
FROM tmp
WHERE school_id = 88888
AND student_id = 8888888;
耗时 9ms
走单列索引
SELECT *
FROM tmp
WHERE student_id = 7777777;
耗时 9ms
多执行几次后，两个查询耗时互有出入
4. 结论
在查询速度上没什么区别。至少在1000万的数据量上很难体现出来。
SQL日志
[2018-11-22 10:53:50] [1287] '@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
sql> USE foo
[2018-11-22 10:53:50] completed in 25 ms
[2018-11-22 10:53:50] [1287] '@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
sql> DROP TABLE IF EXISTS tmp
[2018-11-22 10:53:51] completed in 682 ms
[2018-11-22 10:53:51] [1287] '@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
sql> CREATE TABLE tmp (
id INT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
school_id INT UNSIGNED NOT NULL,
student_id INT UNSIGNED NOT NULL,
INDEX school_id(school_id),
INDEX student_id(student_id),
INDEX school_id_and_student_id(school_id, student_id)
)
[2018-11-22 10:53:51] completed in 45 ms
[2018-11-22 10:53:51] [1287] '@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
sql> DROP PROCEDURE IF EXISTS tmpproc
[2018-11-22 10:53:51] completed in 7 ms
[2018-11-22 10:53:51] [1287] '@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
sql> CREATE PROCEDURE tmpproc() BEGIN
DECLARE i INT UNSIGNED DEFAULT 0;
DECLARE j INT UNSIGNED DEFAULT 0;
WHILE i < 100000 DO
SET i = i + 1;
SET j = 0;
START TRANSACTION;
WHILE j < 100 DO
INSERT INTO tmp (school_id, student_id) VALUES (i, i * 100 + j);
SET j = j + 1;
END WHILE;
COMMIT;
END WHILE;
END
[2018-11-22 10:53:51] completed in 3 ms
[2018-11-22 10:53:51] [1287] '@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
sql> CALL tmpproc()
[2018-11-22 11:02:24] completed in 8 m 32 s 887 ms
[2018-11-22 11:02:24] [1287] '@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
sql> select database()
[2018-11-22 11:02:24] completed in 14 ms
sql> SELECT *
FROM tmp
ORDER BY id DESC
[2018-11-22 11:02:24] 500 rows retrieved starting from 1 in 111 ms (execution: 8 ms, fetching: 103 ms)
[2018-11-22 11:02:24] [1287] '@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
sql> select database()
[2018-11-22 11:02:24] completed in 10 ms
sql> SELECT *
FROM tmp
WHERE school_id = 88888
AND student_id = 8888888
[2018-11-22 11:02:24] 1 row retrieved starting from 1 in 116 ms (execution: 9 ms, fetching: 107 ms)
[2018-11-22 11:02:24] [1287] '@@tx_isolation' is deprecated and will be removed in a future release. Please use '@@transaction_isolation' instead
sql> select database()
[2018-11-22 11:02:24] completed in 7 ms
sql> SELECT *
FROM tmp
WHERE student_id = 7777777
[2018-11-22 11:02:24] 1 row retrieved starting from 1 in 87 ms (execution: 9 ms, fetching: 78 ms)