SQL 常用语句

增删改查 (CRUD)、连接 (JOIN)、建表语法

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数据操作 (DML)

SELECT * FROM table WHERE col = "val"

查询数据

INSERT INTO table (col) VALUES ("val")

插入数据

UPDATE table SET col = "val" WHERE id = 1

更新数据

DELETE FROM table WHERE id = 1

删除数据

连接查询 (JOIN)

SELECT * FROM t1 LEFT JOIN t2 ON t1.id = t2.uid

左连接 (返回左表所有记录)

SELECT * FROM t1 INNER JOIN t2 ON t1.id = t2.uid

内连接 (返回匹配记录)

SELECT * FROM t1 RIGHT JOIN t2 ON t1.id = t2.uid

右连接 (返回右表所有记录)

聚合与排序

SELECT COUNT(*) FROM users

统计行数

SELECT dept, COUNT(*) FROM users GROUP BY dept

分组统计

SELECT dept FROM users GROUP BY dept HAVING COUNT(*) > 10

分组后过滤

SELECT * FROM users ORDER BY created_at DESC LIMIT 20

排序并限制返回条数

数据定义 (DDL)

CREATE TABLE t (id INT PRIMARY KEY, name VARCHAR(50))

创建新表

ALTER TABLE t ADD COLUMN age INT

修改表结构

DROP TABLE table_name

删除表

CREATE INDEX idx_name ON users(name)

创建索引加速查询