如何使用 MyISAM table 加速使用相同 table 与 MySQL 两次的查询？

Question

我使用如下查询，使用两次相同的 table utdat 来恢复数据。

link加2个table的关键是tableA.utprog = tableB.utprog.

SELECT tableA.upd, tableB.utdata  FROM utdat as tableA, utdat AS tableB 
WHERE tableA.uttdat = 'I' AND tableA.utctip = '01' AND   
substring(tableA.utreco, 1, 1) = '3' 
AND tableB.uttdat = 'I' AND tableB.utctip = '01' AND 
substring(tableB.utreco, 1, 1) = '1' 
AND tableA.utprog = tableB.utprog AND TRIM(substr(tableB.utreco, 65, 
12)) = '20000190';

有一种方法可以加快对 MyISAM 数据库的查询速度吗？

Answer 1

在 WHERE 子句中使用的 3 列上创建多列索引：

ALTER TABLE utdat ADD INDEX (uttdat, utctip, itreco);

并将 SUBSTRING(tableA.utreco, 1, 1) = 3 更改为 tableA.utreco LIKE '3%', as MySQL knows how to optimize prefix matching in aLIKEexpression, but it may not realize thatSUBSTR` 正在提取前缀。

它不会影响性能，但你也应该学习 ANSI JOIN 语法。

SELECT tableA.upd, tableB.utdata  
FROM utdat as tableA
JOIN utdat AS tableB ON tableA.utprog = tableB.utprog
WHERE tableA.uttdat = 'I' AND tableA.utctip = '01' AND tableA.utreco LIKE '3%' 
AND tableB.uttdat = 'I' AND tableB.utctip = '01' AND tableB.utreco LIKE '1%' 
AND TRIM(substr(tableB.utreco, 65, 12)) = '20000190';

如何使用 MyISAM table 加速使用相同 table 与 MySQL 两次的查询？

How can I speed up a query that use twice the same table against a MySQL using MyISAM table?

mysql

select

myisam