mysql - 如何在 SQL 存储过程中打印变量？

Question

CREATE DATABASE loan_data;
USE loan_data;
    
CREATE TABLE loan_user (
    id long,
    amount long
    );
    
INSERT INTO loan_user(id, amount)
values (1,7000), (2,7000), (3,5000);

DELIMITER $$
CREATE PROCEDURE loan_check()
BEGIN
DECLARE a int;  
select a = count(amount) from loan_user where amount=7000;
print a;
END $$

DELIMITER ;
CALL loan_check();

DROP DATABASE loan_data;

我想打印 a上面代码中的变量。但是代码返回

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'a;
END' at line 5

如何解决这个问题？

Answer 1

您可以使用 OUT 变量

CREATE TABLE loan_user (
    id long,
    amount long
    );

INSERT INTO loan_user(id, amount)
values (1,7000), (2,7000), (3,5000);

CREATE PROCEDURE loan_check(OUT _answer BIGINT)
BEGIN
DECLARE a int;  
select  count(amount) into a from loan_user where amount=7000;
SET _answer =  a;
END

SET @answer := 0;
CALL loan_check(@answer);
SELECT IF(@answer = 2, 'yes',@answer)as answer

✓

✓

| answer |
| :----- |
| yes    |

db<> fiddle here *
或者干脆不要使用 INTO 或 :=

CREATE TABLE loan_user (
    id long,
    amount long
    );

INSERT INTO loan_user(id, amount)
values (1,7000), (2,7000), (3,5000);

CREATE PROCEDURE loan_check()
BEGIN
DECLARE a int;  
select  count(amount)  from loan_user where amount=7000;

END

CALL loan_check();

| count(amount) |
| ------------: |
|             2 |

✓

CREATE PROCEDURE loan_check2(_inc int)
BEGIN
DECLARE a int;  
select  IF(count(amount) = 2 , 'yes',COUNT(amount)) as answer from loan_user where amount=_inc;

END

CALL loan_check2(7000);

| answer |
| :----- |
| yes    |

✓

db<> fiddle here