How to assign value to mysql stored procedure

MySQL stored procedure is a set of SQL statements stored in the MySQL database. It can be executed and called like a function. One of the important functions is to pass the values ​​of variables to stored procedures. These variables can be input parameters or output parameters. In MySQL stored procedures, assignment is a very important concept. This article will introduce MySQL stored procedures from the perspective of assignment.

1. The basic writing method of assignment in stored procedures

The assignment statements in stored procedures are mainly implemented by SET and SELECT statements. Among them, the SET statement is used to assign the value of a variable or expression to another variable or expression; the SELECT statement can be used to query specific values ​​in the database and assign them to variables. The following are introduced separately:

1.SET statement

The basic syntax of the SET statement is as follows:

SET variable_name = expression;

Among them, variable_name represents the current The name of the assigned variable, expression represents the value assigned to the variable. Here are some specific examples:

-- Assign the number 1 to the variable a
SET a = 1;

-- Assign the string 'hello' to the variable b
SET b = 'hello';

-- Assign the result of the mathematical operation to the variable c
SET c = 2 * (3 4);

2.SELECT statement

## The basic syntax of the #SELECT statement is as follows:

SELECT column_name INTO variable_name FROM table_name WHERE condition;

Among them, column_name represents the column name that needs to be queried, variable_name represents the variable name that accepts the query results, and table_name represents The name of the table that needs to be queried, and condition represents the condition that needs to be queried. The following is a specific example:

-- Query the name column in the user table and assign it to the variable name

SELECT name INTO name FROM user WHERE id = 1;

二, Application of assignment in stored procedures

1. Assign query results to variables

Some query operations are often required in stored procedures, such as counting quantities, averaging, etc. At this time, you can use the SELECT statement to assign the query results to variables, and then perform subsequent logical processing. The following is an example of averaging:

-- Query the average score of all students in the score table and assign it to the variable avg

SELECT AVG(score) INTO avg FROM score;

2. Assign values ​​between variables

In the stored procedure, assignment operations between variables also need to be performed. In this case, the SET statement can be used to achieve this. The following is an example of concatenating string variables:

-- concatenate string variables s and t together and assign them to u

SET u = CONCAT(s, t);

3. Use the IF statement to implement assignment

The IF statement is a conditional statement often used in stored procedures, which can perform different operations based on different conditions. If you need to assign a value to a variable based on conditions, you can use the IF statement to assign the value. The following is an example of returning different values ​​based on conditional judgment:

--If a is greater than b, assign 1 to variable c, otherwise assign 2 to variable c

IF a > b THEN

SET c = 1;

ELSE

SET c = 2;

END IF;

3. Summary

In MySQL stored procedures, assignment is a very important concept. Use the SET and SELECT statements to assign values ​​between variables and assign query results to variables. At the same time, the IF statement can also implement variable assignment operations based on different conditions. When writing stored procedures, use appropriate assignment statements to implement logical processing, thereby improving the quality and efficiency of the code.

The above is the detailed content of How to assign value to mysql stored procedure. For more information, please follow other related articles on the PHP Chinese website!