How to use if nested statements in MySQL stored procedures

MySQL stored procedures are code blocks composed of a series of SQL statements that can perform complex operations in the database. In stored procedures, the if statement is a frequently used branch structure statement that can perform different operations based on conditions. This article will introduce how to use if nested statements in MySQL stored procedures.

1. Introduction to if statement

The if statement is a branching structure statement that performs different operations based on conditions. The if statement usually consists of a conditional expression and one or more statements. If the value of the conditional expression is true, then the statements in the if statement are executed; otherwise, the if statement block is skipped.

The syntax of the if statement is as follows:

if(condition)then
    statement;
else
    statement;
end if;

Among them, condition is the conditional expression, and statement is the SQL statement that needs to be executed.

2. Introduction to if nested statements

The if nested statement refers to nesting one or more if statement blocks within an if statement block for execution based on different conditions. different operations. The syntax of if nested statements is as follows:

if(condition1)then
    statement;
    if(condition2)then
        statement;
    else
        statement;
    end if;
else if(condition3)then
    statement;
else
    statement;
end if;

Among them, condition1 is the conditional expression of the first level if; condition2 is the conditional expression of the second level if; condition3 is the conditional expression of the first else if ;statement is the SQL statement that needs to be executed.

3. Example of nested if statements

The following is an example of a stored procedure using nested if statements:

delimiter //
create procedure test_if_nested(
    in student_name varchar(50),
    out result_msg varchar(50)
)
begin
    declare student_score int;
    select score into student_score from student where name = student_name;
    if(student_score >= 90)then
        set result_msg = '优秀';
        if(student_score = 100)then
            set result_msg = concat(result_msg, '，满分');
        end if;
    else if(student_score >= 60)then
        set result_msg = '及格';
    else
        set result_msg = '不及格';
    end if;
end //
delimiter ;

This stored procedure is used to judge students based on their scores Score:

1. If the score is greater than or equal to 90 points, it is considered excellent. If it is 100 points, "full score" is added;
2. If the score is greater than or equal to 60 points, it is considered passing. ;
3. If the score is less than 60 points, it will be a failure.

4. Stored procedure call

The stored procedure can be called through the call command. The syntax is as follows:

call procedure_name(argument1, argument2, ...);

Among them, procedure_name is the name of the stored procedure, argument1, argument2, etc. are parameters of the stored procedure.

For example, to call the stored procedure above, you can use the following command:

call test_if_nested('张三', @result_msg);
select @result_msg as result;

Pass in a student name parameter and output the result through the out parameter. The result is as follows:

+-------------+
| result      |
+-------------+
| 及格       |
+-------------+

Through the above calling method, we can obtain the student's score based on his name and judge the student's grade based on the score.

Summary:

The MySQL stored procedure if nested statement can be used to determine different conditions and perform different operations when the conditional branch is complex. By using stored procedures, we can complete complex business logic calculations in MySQL, improving program operation efficiency and database security.

The above is the detailed content of How to use if nested statements in MySQL stored procedures. For more information, please follow other related articles on the PHP Chinese website!