在MySQL中优化依赖子查询的索引
在MySQL中优化依赖子查询的索引
提问于 2018-07-20 00:20:46
我有一个包含依赖子查询的查询，我想知道应该为哪些字段建立索引以获得最高性能？例如，下面的查询显示了姓名中包含"smi“的所有订单。该查询通过orders和customer表中的shared cust#从customer表中获取客户名称。我被这个查询卡住了，因为它大多是由php开发工具自动生成的。那么，考虑到这些约束，应该索引哪些字段才能获得最佳性能呢？
SELECT *, (SELECT CONCAT(customers.last, ', ', customers.first)
FROM customers WHERE customers.cust_num = orders.cust_num) AS c_lastname
FROM orders WHERE (SELECT CONCAT(customers.last, ', ', customers.first)
FROM customers WHERE customers.cust_num = orders.cust_num) LIKE '%smi%'
ORDER BY order_id DESC LIMIT 0, 20EXPLAIN告诉我：
"1" "PRIMARY" "orders" "index" \N "PRIMARY" "4" \N "20" "Using where"
"3" "DEPENDENT SUBQUERY" "customers" "eq_ref" "PRIMARY" "PRIMARY" "4" "orders.cust_num" "1" ""
"2" "DEPENDENT SUBQUERY" "customers" "eq_ref" "PRIMARY" "PRIMARY" "4" "orders.cust_num" "1" ""页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/51427577
复制相关文章
相似问题