SQL 基础语句

一些最重要的 SQL 命令

btw,SQL 对大小写不敏感

• SELECT - 从数据库提取数据

SELECT column_name(s)
FROM table_name
WHERE condition
ORDER BY column_name [ASC|DESC]

• INSERT INTO - 向数据库中插入新数据

INSERT INTO table_name (column1, column2, ...)
VALUES (value1, value2, ...)

• UPDATE - 更新数据库中的数据

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition

• DELETE - 从数据库表中删除数据

DELETE FROM table_name
WHERE condition

• DROP - 删除数据库对象，如表、视图、索引等

DROP TABLE table_name;
DROP DATABASE database_name;
DROP VIEW view_name;

• CREATE INDEX - 创建索引，以加快查询速度

CREATE INDEX index_name
ON table_name (column1, column2, ...);

• WHERE - 指定筛选条件

SELECT column_name(s)
FROM table_name
WHERE condition

• ORDER BY - 对结果集进行排序

SELECT column_name(s)
FROM table_name
ORDER BY column_name [ASC|DESC] -- ASC: 升序，DESC: 降序

• GROUP BY - 将结果集按一列或多列进行分组

SELECT column_name(s), aggregate_function(column_name)
FROM table_name
WHERE condition
GROUP BY column_name(s)

• HAVING - 对分组后的结果集进行筛选

SELECT column_name(s), aggregate_function(column_name)
FROM table_name
GROUP BY column_name(s)
HAVING condition

• JOIN - 将两个或多个表的记录结合起来

SELECT column_name(s)
FROM table_name1
JOIN table_name2
ON table_name1.column_name = table_name2.column_name

• DISTINCT - 返回唯一不同的值

SELECT DISTINCT column_name(s)
FROM table_name