sql基础教程
简介
- SQL:structured query language,结构化查询语言
- RDBMS:relational database management system,关系型数据库管理系统
基本语句
① SELECT
SELECT column_name1,column_name2 FROM table_name; --按列名查询
SELECT * FROM table_name; --全列查询
-- DISTINCT(查询唯一值)
SELECT DISTINCT column_name FROM table_name;
-- WHERE(条件查询)
SELECT column_name FROM table_name WHERE column_name? operator value;
-- =:数值没有'',字符串有''
-- <>/!=:不等
-- IS NULL/IS NOT NULL:IS仅用在判断NULL上
-- </>/<=/>=
-- BETWEEN a AND b:[a,b]中的值
-- IN (?,?...):在可能值之中
-- LIKE:模糊匹配,_通配一个字符,%通配0或多个字符
-- AND/OR/NOT:逻辑操作符
-- ORDER BY(查询结果排序)
SELECT column_name FROM table_name ORDER BY column_name ASC/DESC; --对一列排序输出,默认ASC
SELECT column_name1,column_name2 FROM table_name ORDER BY column_name1 ASC/DESC,column_name2 ASC/DESC; --在column_name1排序的基础上,对column_name2排序
② INSERT
INSERT INTO table_name VALUES (value1,value2,...); --需要所有字段的值
INSERT INTO table_name (column_name1,column_name2,...) VALUES (value1,value2,...); --添加指定字段
③ UPDATE(配合WHERE)
UPDATE table_name SET column_name1=value1,column_name2=value2... WHERE some_column=some_value;
④ DELETE
DELETE FROM table_name WHERE some_column=some_value; --删除指定列
DELETE FROM table_name; --删除表中内容(不删除表)
DELETE * FROM table_name; --同上