SQL语法整理

Posted 2021-02-01 Aquarium

1.CREATE
创建数据库：CREATE DATABASE db_name
创建表：CREATE TABLE table_name (col_name col_type [NOT NULL] [PRIMARY KEY], ...)

2.DROP
删除表：DROP TABLE table_name

3.ALTER
添加列：ALTER TABLE table_name ADD COLUMN col_type
添加主键：ALTER TABLE table_name ADD PRIMARY KEY(col_name)

4.INSERT
插入记录：INSERT INTO table_name (col_name, ...) VALUES (col_value, ...)

5.DELETE
删除记录：DELETE FROM table_name WHERE col_name=col_value
*safe update模式只能通过主键字段更新记录，更新同理

6.UPDATE
更新记录：UPDATE table_name SET col_name=col_value, ... WHERE ...

7.SELECT
查询部分字段：SELECT col_name, ... FROM table_name WHERE ...
查询全部字段：SELECT * FROM table_name WHERE ...

8.OUTER JOIN (表)
table_name1 LEFT/RIGHT OUTER JOIN table_name2
*左联查询把table1的内容全部查出，table2中只查出满足条件的内容，其他为null

9.INNER JOIN （表）
table_name1 INNER JOIN table_name2 ON table_name1.col_name1=table_name2.col_name2
*只查出满足条件的记录

10.ORDER BY
升序：SELECT ... ORDER BY col_name
降序：SELECT ... ORDER BY col_name DESC

11.聚合函数（字段）
和：sum(col_name)
平均：avg(col_name)
最大：max(col_name)
最小：min(col_name)
计数：count(col_name)

12.GROUP BY
某字段同值记录合并：GROUP BY col_name
eg. SELECT sum(col_name2) as new_col_name FROM table_name GROUP BY col_name