SQL优化建议备忘录_MySQL
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SQL优化建议备忘录
1、SQL注释一般不会增加性能开销，并且可以增强可读性
2、事务宜简短
3、避免游标操作
因为游标占用大量的资源
4、IN和EXISTS的权衡
5、避免嵌套视图和在单表检索时避免指向多个表的视图
6、DISTINCT和ORDER BY开销
完全可以在应用程序中进行处理
7、尽量为每一列设置默认值，并且NOT NULL。因为包含NULL值的列不能利用索引，即使你创建了索引。使用了IS NULL和IS NOT NULL的查询也不会使用索引
8、海量查询避免类型转换
9、为外键关联的列建立索引
10、UNION与UNION ALL，后者效率更高
11、INSERT语句
INSERT INTO table VALUES (…)性能差于INSERT INTO table (…) VALUES (…)
12、使用ORDER BY时的注意事项
任何在ORDER BY中的非索引项或者计算表达式都将降低查询效率
13、BETWEEN与IN的权衡
…
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