一、執行計劃一些參考鏈接
mysql explain type連接類型示例
MySQL EXPLAIN SQL 輸出信息描述
二、獲取SQL執行計劃
方法1(命令行):EXPLAIN sql_statement
方法2(Toad):Toad裏邊在SQL編輯器裏邊點擊explain plan
方法3(Navicate)Navicate裏邊點擊解釋
三、案例
1、原始SQL及完整執行計劃
原始SQL語句:
SELECT c.customerNumber, c.customerName, e.lastname
FROM customers c
INNER JOIN employees e ON c.salesRepEmployeeNumber = e.employeeNumber
WHERE e.lastname LIKE 'T%'
AND EXISTS
(SELECT orderNumber, SUM(priceEach * quantityOrdered)
FROM orderdetails INNER JOIN orders USING (orderNumber)
WHERE customerNumber = c.customerNumber
GROUP BY orderNumber
HAVING SUM(priceEach * quantityOrdered) > 50000)
UNION
SELECT customerNumber, customerName, 'NULL'
FROM customers
WHERE customerName LIKE 'T%'
執行計劃截圖
2、執行計劃包含的信息 – id列
3、執行計劃包含的信息 – select_type列
4、執行計劃包含的信息 – table列
5、執行計劃包含的信息 – type列cost對比
type列示例