mysql 查询中括号

SELECT column1, COUNT(column2) 
FROM table_name 
GROUP BY (column1, column2);

SELECT column1 
FROM table1 
WHERE column1 IN (SELECT column2 FROM table2);

SELECT (column1 + column2) AS total 
FROM table_name;

-- 错误示例
SELECT column1 FROM table_name WHERE (column1 = 'value';

-- 正确示例
SELECT column1 FROM table_name WHERE (column1 = 'value');

-- 错误示例
SELECT column1 FROM table1 WHERE column1 IN (SELECT column2 FROM table2 WHERE column3 = 'value');

-- 如果table2中没有column3为'value'的行，子查询将返回空集，导致外层查询也返回空集。
-- 解决方法：确保子查询条件正确。

-- 使用JOIN代替子查询
SELECT t1.column1 
FROM table1 t1 
JOIN table2 t2 ON t1.column2 = t2.column2 
WHERE t2.column3 = 'value';