Three uses and differences of MySQL not equal

Judgment symbols are often used in MySQL, and not equal to is a more commonly used symbol . The following three not equal to symbols are explained

MySQL recommends using <> to indicate inequality . Why? Because of its strong portability and fast query speed . There is a question on LeetCode, which is a movie theater query question. The title is as follows:

In fact, it is very simple. You can query descriptions that are not boring and ids that are not even numbers, and sort the query results using order by. However, when querying descriptions that are not boring, you need to use the not equal to judgment. The following is a comparison of the query time I used three not equal to

It can be seen that <> is still faster, so it is recommended to use <> to indicate inequality.

There is no point in saying more, let’s give an example! ! !

A simple table data:

select * from user where address != "北京" 

select * from user where address <> "Beijing"

select * from user where address = null

select * from user where address is null

select * from user where address != null

Summarize:

select * from user where address != "北京"
 
select * from user where address <> "Beijing"
 
select * from user where address = null
select * from user where address is null
 
select * from user where address != null
select * from user where address is not null

Just a few sentences and three extremely common points, perhaps we are at a loss and hesitant when answering.

In <> and! = are equivalent. When a field is not equal to a certain value (a non-empty value), the output result is that this field is empty and not output.

is and is not are used in conjunction with null . I call it is not, not empty.

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