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手机空号过滤,提高工作效率

秀妮_5519 2024-05-02 阅读 12

文章目录

查找:生产ID为DTNTR物品的供应商,生产的其他物品。

子查询
SELECT
	prod_id,
	prod_name 
FROM
	products 
WHERE
	vend_id = ( SELECT vend_id FROM products WHERE prod_id = 'DTNTR' );

image-20240501114920671

自联结
SELECT p1.prod_id,p1.prod_name   # 必须指定为p1.prod_id,p1.prod_name
FROM
	products AS p1,
	products AS p2 
WHERE
	p1.vend_id = p2.vend_id 
	AND p2.prod_id = 'DTNTR'

image-20240501115457088

比较

从运行时间看,自联结比子查询快!

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