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))
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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'
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4.修改语句
UPDATE t_test SET title_ = '标题改',content_='内容改' WHERE id_='1'
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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
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6.表增加字段
ALTER TABLE t_test ADD click_num_ VARCHAR(10)
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7.类型转换+求和
SELECT SUM(CAST(id_ AS DECIMAL)) FROM t_test
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8.判空 IFNULL(column,value)
SELECT IFNULL(SUM(CAST(click_num_ AS DECIMAL)),0) FROM t_test
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9.IF NOT EXISTS+NOT NULL（不为空）+UNIQUE（唯一）
CREATE TABLE IF NOT EXISTS t_test ( id_ VARCHAR(32) NOT NULL UNIQUE, title_ VARCHAR(255), content_ VARCHAR(2000), create_time_ VARCHAR(25), state_ VARCHAR(10) )
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10.去掉重复数据 ? ? ?DISTINCT
SELECT DISTINCT title_,content_ FROM t_test1
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11.表信息查询
SELECT * FROM information_schema.columns WHERE table_schema='cxy' AND table_name='t_test' AND column_name='title_';
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12.删除表
DROP TABLE t_test
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13.字符串连接
SELECT CONCAT(title_,':',content_) AS 标题文章 FROM t_test
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14.截取字符串 ? ?LEFT(str,len)、RIGHT(str,len)、SUBSTRING(str,pos,len)
SELECT LEFT(content_,2) FROM t_testSELECT RIGHT(content_,2) FROM t_testSELECT SUBSTRING(content_,2,1) FROM t_test
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15.数据库信息语句
SELECT VERSION(),USER(),DATABASE();
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16.字段表达式
SELECTid_ 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：3.3000000000000003SELECTid_ AS id,'正常' AS 状态,CONVERT((id_*1.1),DECIMAL(10,2)) AS 主键转换 FROM t_test;
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17.类型转换
#CAST(xxx AS 类型) , CONVERT(xxx,类型)SIGNED:整数SELECT CONVERT('23.1',SIGNED);#结果：23SELECT CONVERT('23.9',SIGNED);#结果：23SELECT 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
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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
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#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;
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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asSELECT t.id_,t.title_ FROM t_test t;SELECT t.id_,t.title_ FROM t_test AS t;
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21.and、or、not、between and/is null
# where 中的 and、or、not、between and/is nullSELECT * 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'
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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_) > 2GROUP 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;
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23.排序
#ORDER BYSELECT * 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
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24.不等于
SELECT * FROM t_test WHERE id_ != '1';SELECT * FROM t_test WHERE id_ <> '1';
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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%';
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