How does mysql determine that the field is empty?

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Here are five ways to query:

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

When the query condition is null, replace it with the specified character

Select name, isfull (gender,' unknown') as gender from users where email = 'xxxx'

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