mysql - 使用 IF 语句更新查询

Question

我需要创建一个带有IF语句的 MySQL 查询。这是一个数据库模式：

CREATE DATABASE my_db;
USE my_db;
CREATE TABLE IF NOT EXISTS if_table(
    id INTEGER unsigned,
    field_1 INTEGER unsigned,
    field_2 INTEGER unsigned,
    field_3 INTEGER unsigned,
    PRIMARY KEY (id)
);

如何编写UPDATE对应于下一个伪代码的查询？

if field_2 equals 0 then field_1 = field_1 + 1
else field_3 = field_3 + 2 
where id == 1

Answer 1

试试这个内联IF语句

SELECT IF(field_2 = 0, field_1 + 1, field_3 + 2) AS `Result`
FROM tableName
WHERE ID = 1

或者如果你想更新值，

UPDATE tableName
SET field_1 = IF(field_2 = 0, field_1 + 1, field_1),  
    field_3 = IF(field_2 = 0, field_3, field_3 + 2)
WHERE ID = 1

Answer 2

你可以用两个查询来做到这一点。

UPDATE table_name SET field_1 = field_1 + 1 WHERE id = 1 AND field_2 = 0;
UPDATE table_name SET field_3 = field_3 + 2 WHERE id = 1 AND field_2 != 0;

如果您只想要一个查询，那么

UPDATE table_name
SET field_1 = IF(field_2 = 0, field_1 + 1, field_1),
SET field_3 = IF(field_2 = 0, field_3, field_3 + 2),
WHERE ID = 1