Summary of the use of special operators in MySql

Preface

There are 4 types of operators in MySQL, they are:

• Arithmetic operators
• Comparison Operators
• Logical operators
• Bitwise operators

This should be familiar to everyone, but this article summarizes the relevant content about special operators in MySQL. Let's take a look at the detailed introduction.

1. <=> safe comparison operator

In MySQL, any comparison with NULL will be NULL, which is often used to determine whether it is NULL.

Of course I can also use IS NULL

2. The role of := assignment

Both the := and = operators have the function of assigning values. In most scenarios, there is no difference between them, but := is more applicable to all scenarios.

= has the same function as := only when used for set and update, i.e. assignment. Otherwise, it functions as the relational operator equal to.

:= is not only used for setting and updating, but also for selecting. It is often used in combination with @, such as numbering.

3. @ User variables

@ is a local variable declaration. If there is no @, the field represents the column name and is used for user variable declaration.

4. @@ System variables

System variables are divided into global system variables and session system variables

Some system variables are only available at the global level, such as max_connnections. You do not need to explicitly declare global when reading, but you need to declare when setting. Otherwise, you will be prompted to set a global variable.

These are the most commonly used ones, and I will add more later. . .

Summarize

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