Question

关于SQL DELETE嵌套子查询问题

我要删除一个名为stock表中manu_code代码为145378的那一行,我可以这样写:
DELETE FROM stock
WHERE stock.manu_code = '145378'
这样肯定是没什么问题的,
但是现在我偏偏要嵌套一个子查询,改写:
DELETE FROM stock
WHERE 1 = (
SELECT COUNT(*)
FROM stock
WHERE stock.manu_code = '145378'
)
两个不是等价吗,为什么后面的那个不行啊
查资料是说:DELETE语句中的WHERE子句不能使用一个判断同样的表的子查询,那好,我想知道为什么.
先谢过.

Answer 1

子查询：SELECT COUNT(*)FROM stock WHERE stock.manu_code = '145378'的返回值如果是1的话，你的SQL就会是：
DELETE FROM stock WHERE 1 = 1
那么就会把所有数据删除的，所以SQL可以如下：
DELETE FROM stock WHERE 1 = (SELECT COUNT(*) FROM stock WHERE stock.manu_code = '145378') AND stock.manu_code = '145378'

Answer 2

DELETE FROM stock
WHERE 1 = (
SELECT COUNT(*)
FROM stock
WHERE stock.manu_code = '145378'
)
似乎等价于DELETE FROM stock WHERE 1 = 1
另外楼主真有钻牛角尖的精神，期待其他答案

Answer 3

两个不等价
第一个是删除 stock.manu_code = '145378'这些记录。
第二个只要条件成立(count(*)=1)，就删除所有记录。