计算Null记录不起作用

Question

create table scoda(product varchar(25),price int,sale varchar(23))
insert into scoda values('watch',10,6)
insert into scoda values('socks',8,'NULL')

SELECT COUNT(*) AS GK FROM scoda WHERE sale IS NULL

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Expected output:1
Actual output:0

需要帮助才能继续我在sql初学者

Answer 1

USE

insert into scoda values('socks',8,NULL)

（不含引号）。

Answer 2

问题在于插入语句：

insert into scoda values('socks',8,NULL)