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How to add serial number to query in mysql

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Release: 2022-03-09 15:33:51
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In mysql, you can use the SELECT statement to define user variables to add serial numbers to the query results. The syntax is "SELECT field 1, field 2, (@i:=@i 1) AS 'serial number' FROM table name, (SELECT @i:=0) AS itable;".

How to add serial number to query in mysql

The operating environment of this tutorial: windows10 system, mysql8.0.22 version, Dell G3 computer.

How to add serial numbers to queries in mysql

A common solution is to generate serial numbers by defining user variables

Example: Assume that the database has a student table

There are fields in the table: sid, sname, gender, age

Query the data in the table and add the serial number. The corresponding SQL is:

SELECT sid,sname,gender,age,(@i:=@i+1) AS '序号' 
FROM student,(SELECT @i:=0) AS itable;
Copy after login

or

SET @i=0;
SELECT sid,sname,gender,age,@i:=@i+1 AS '序号' 
FROM student;
Copy after login

The query results are as shown in the figure:

How to add serial number to query in mysql

Explanation:

1, (@i:=@i 1) can also be written as @i: =@i 1, parentheses are added for visual clarity.

What it means is: add 1 to variable i and assign it to variable i. After defining a variable, the variable will be incremented every time you query. This variable is not needed every time you execute the query statement to obtain the results. Added

2, (SELECT @i:=0) AS itable, defines user variable i, sets the initial value to 0, and then uses it as a derived table. AS defines the alias of the table.

3. SET @i=0. Define user variable i and assign the initial value to 0.

Related knowledge points:

1. How MySQL defines user variables: select @variable name. In the above SQL statement, the name of the variable Yes i

2. User variable assignment: one is to use the "=" sign directly, and the other is to use the ":=" sign. The difference between

= and :=:

When using the set command to assign values ​​to user variables, both methods can be used,

That is: SET @variable name=xxx Or SET @variable name:=xxx

When using the select statement to assign a value to a user variable, you can only use the ":=" method, because in the select statement, the "=" sign is regarded as a comparison operator . That is: SELECT @variable name:=xxx

①: User variable

②: Derived table

③: AS setting alias

is written in Oracle Yes:

SELECT "sid","sname","gender","age",
ROW_NUMBER() over(order by "sid") AS "序号"
FROM "user";
Copy after login

Recommended learning: mysql video tutorial

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