mysql怎么判断字段为空

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这里提供了5种方法进行查询：

isnull()

select * from users where email = 'xxxx' and isnull(deletedAt)

is null

select * from users where email = 'xxxx' and deletedAt is null

is not null

select * from users where email = 'xxxx' and deletedAt is not null

!isnull()

select * from users where email = 'xxxx' and !isnull(deletedAt) 
select * from users where email = 'xxxx' and not isnull(deletedAt)

isfull

当查询条件为 null，用指定字符替代

select name,  isfull(gender,'未知') as gender  from users where email = 'xxxx'

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