How to determine whether a field is empty in mysql

Mysql method to determine whether a field is empty: You can use the isnull() function to determine. The specific code is [select * from users where email = 'xxxx' and isnull(deletedAt)].

MySQL is a relational database management system developed by the Swedish MySQL AB company and is currently a product of Oracle. MySQL is one of the most popular relational database management systems. In terms of WEB applications, MySQL is the best RDBMS (Relational Database Management System) application software.

(Recommended tutorial: mysql video tutorial)

When we need to know whether a certain field in mysql is empty? How to achieve it?

Here are 5 methods for querying:

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,'未知') as gender  from users where email = 'xxxx'

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