mysql查询结果返回

-- 检查查询条件
SELECT * FROM table_name WHERE condition;

-- 确认表中有数据
SELECT COUNT(*) FROM table_name;

-- 添加索引
ALTER TABLE table_name ADD INDEX index_name (column_name);

-- 优化查询语句
SELECT * FROM table_name WHERE column_name = 'value' LIMIT 10;

-- 使用事务
START TRANSACTION;
UPDATE table_name SET column1 = value1 WHERE condition1;
UPDATE table_name SET column2 = value2 WHERE condition2;
COMMIT;

-- 简单查询
SELECT * FROM users;

-- 条件查询
SELECT * FROM users WHERE id = 1;

-- 排序查询
SELECT * FROM users ORDER BY name ASC;

-- 分组查询
SELECT email, COUNT(*) FROM users GROUP BY email;

-- 连接查询
SELECT users.name, orders.order_id
FROM users
JOIN orders ON users.id = orders.user_id;