isnull()select * from users where email = 'xxxx' and isnull(deletedAt)
is nullselect * from users where email = 'xxxx' and deletedAt is null
is not nullselect * 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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