常用sql语句 -- mysql

总结一下常用的sql语句，测试版本：5.1

1.创建表

CREATE TABLE t_test
(
	id_ VARCHAR(32),
	title_ VARCHAR(255),
	content_ VARCHAR(2000),
	create_time_ VARCHAR(25),
	state_ VARCHAR(10)
)

2.插入语句

INSERT INTO t_test  VALUES ('1', '标题','内容','2013-01-30','1')
INSERT INTO t_test (id_,title_,state_) VALUES ('2', '标题2','0')

3.删除语句

DELETE FROM t_test WHERE id_='2'

4.修改语句

UPDATE t_test SET title_ = '标题改',content_='内容改' WHERE id_='1'

5.查询语句

SELECT * FROM t_test WHERE id_='1'
SELECT title_ AS 标题,content_ AS 内容 FROM t_test WHERE id_='1'
SELECT * FROM t_test LIMIT 2,3 //从序号2开始，查3条记录，做翻页最简单

6.表增加字段

ALTER TABLE t_test ADD click_num_ VARCHAR(10)

7.类型转换+求和

SELECT SUM(CAST(id_ AS DECIMAL)) FROM t_test

8.判空 IFNULL(column,value)

SELECT IFNULL(SUM(CAST(click_num_ AS DECIMAL)),0) FROM t_test

9.IF NOT EXISTS+NOT NULL（不为空）+UNIQUE（唯一）+PRIMARY KEY（主键）

CREATE TABLE IF NOT EXISTS t_test  
(  
    id_ VARCHAR(32) NOT NULL UNIQUE PRIMARY KEY,  
    title_ VARCHAR(255),  
    content_ VARCHAR(2000),  
    create_time_ VARCHAR(25),  
    state_ VARCHAR(10)  
)

10.去掉重复数据 DISTINCT

SELECT DISTINCT title_,content_ FROM t_test1

11.表信息查询

SELECT * FROM information_schema.columns WHERE table_schema='cxy' AND table_name='t_test' AND column_name='title_';

12.删除表

DROP TABLE t_test

13.字符串连接

SELECT CONCAT(title_,':',content_) AS 标题文章 FROM t_test

14.截取字符串 LEFT(str,len)、RIGHT(str,len)、SUBSTRING(str,pos,len)

SELECT LEFT(content_,2) FROM t_test
SELECT RIGHT(content_,2) FROM t_test
SELECT SUBSTRING(content_,2,1) FROM t_test

15.数据库信息语句

SELECT VERSION(),USER(),DATABASE();

16.字段表达式

SELECT	id_ AS id,'正常' AS 状态,(id_*1.1) AS 主键转换 FROM t_test; 
#会出现异常数据，类似：3.3000000000000003
SELECT	id_ AS id,'正常' AS 状态,CONVERT((id_*1.1),DECIMAL(10,2)) AS 主键转换 FROM t_test;

17.类型转换

#CAST(xxx  AS   类型) , CONVERT(xxx,类型)	SIGNED:整数
SELECT CONVERT('23.1',SIGNED);	#结果：23
SELECT CONVERT('23.9',SIGNED);	#结果：23
SELECT CONVERT('23.1',DECIMAL(4,2));	#DECIMAL(2+2,2)，第一个参数是小数点前和小数点后的和值，第二个参数是小数点后的值
SELECT LEFT(CONVERT(100.1,CHAR),2);

SELECT CAST('23.911' AS DECIMAL(4,2));	#结果：23.91

18.注意：distinct 会先排序，对于大的结果集来说是相当耗时的

19.表广泛的定义有：永久表（create table）、临时表（子查询所返回的表）、虚拟表（create view）

SELECT t_temp.标题,t_temp.内容 FROM
(SELECT id_, title_ AS 标题,content_ AS 内容 FROM t_test) AS t_temp;	#t_temp 就是临时表

视图：

#创建试图不能包含子查询
CREATE VIEW t_simple_test AS 
SELECT SUM(id_) FROM t_test;

SELECT * FROM t_simple_test;

DROP VIEW t_simple_test;

20.简化表名

#可以使用表别名 来简化长表明 可以直接写别名，也可以 使用as
SELECT t.id_,t.title_ FROM t_test t;
SELECT t.id_,t.title_ FROM t_test AS t;

21.and、or、not、between and/is null

# where 中的 and、or、not、between and/is null
SELECT * FROM t_test WHERE NOT(id_='1');
SELECT * FROM t_test WHERE title_ IS NOT NULL AND id_='2' OR id_='3';
SELECT * FROM t_test WHERE create_time_ BETWEEN '2012-12-01' AND '2013-01-31'

22.group by 和having

#having 能对分组后的数据进行筛选，尤其在使用聚集函数的时候
SELECT create_time_,SUM(click_num_) AS num FROM t_test 
WHERE SUM(click_num_) > 2
GROUP BY create_time_ ;	#这个查询是会报错的

SELECT create_time_,SUM(click_num_) AS num FROM t_test 
GROUP BY create_time_ HAVING num > 2;

23.排序

#ORDER BY
SELECT * FROM t_test ORDER BY click_num_;	#从小到大
SELECT * FROM t_test ORDER BY click_num_ DESC;	#从大到小
SELECT * FROM t_test ORDER BY click_num_ ,id_;	#多排序

24.不等于

SELECT * FROM t_test WHERE  id_ != '1';
SELECT * FROM t_test WHERE  id_ <> '1';

25.in 和 not in

SELECT * FROM t_test WHERE title_ IN('标题1','标题2');
SELECT * FROM t_test WHERE id_ IN(SELECT id_ FROM t_test WHERE click_num_ >3);
SELECT * FROM t_test WHERE id_ NOT IN(SELECT id_ FROM t_test WHERE click_num_ >3);

26.like 和通配符

SELECT * FROM t_test WHERE title_ LIKE '标题_';
SELECT * FROM t_test WHERE title_ LIKE '%题%';

27.临时事务

BEGIN;  #开始事务
INSERT INTO t_test  VALUES ('11', '标题11','内容11','2013-01-30','1',1);  
SELECT * FROM t_test;  #这里的查询是有上面的记录的，但是实际库中并没有这个记录
ROLLBACK;  #回滚

常用sql语句 -- mysql

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