MySql常用sql语句

Hive中的mysql取前一个月的日期

SELECT
a.xh AS student_number,
concat( substring( a.DAYS, 1, 11 ), a.STARTTIME ) AS starttime,
a.S_NAME AS coursename,
'1' AS STATUS
FROM
XJ_WATERLIST_TO_DC a
WHERE
a.STATUS = '3'
AND substring( a.days, 1, 7 ) BETWEEN from_unixtime( unix_timestamp( ) - 2678400, 'yyyy-MM-dd' )
AND from_unixtime( unix_timestamp( ), 'yyyy-MM-dd' )
ORDER BY
substring( starttime, 1, 10 )

mysql字符串向前匹配12个月

SELECT * FROM student_all_closeclasswarning a
where substring( a.starttime, 1, 10 ) between DATE_SUB(CURDATE(), INTERVAL 12 MONTH) and substring(now(),1,10);

查看mysql的版本

select version();

导出数据库中的某个表的数据

mysqldump -u userName -p  dabaseName tableName > fileName.sql

举例：

mysqldump -u root -p bigdata_web_statis studygrade > /home/studygrade.sql

如果想在一个已经建好的表中添加一列

alter table t1 add column addr varchar(20) not null;

举例：

alter table averager_grade add xf varchar(255) not null;

MySQL将查询结果插入到数据表中

INSERT INTO student(id,xuesheng,yuwen,shuxue,yingyu)
SELECT id,xuesheng,yuwen,shuxue,yingyu FROM stu;

截取前12个月的日期

substring( a.starttime, 1, 10 ) between DATE_SUB(CURDATE(), INTERVAL 12 MONTH) and substring(now(),1,10);

查询一个结果放
4000
到另一张表中去

insert into student_closeclasswarning_recent SELECT * FROM student_all_closeclasswarning a

建表时指定索引和编码格式

CREATE TABLE `student_closeclasswarning_recent` (
`student_number` varchar(250) DEFAULT NULL COMMENT '学号',
`starttime` varchar(250) DEFAULT NULL COMMENT '旷课时间',
`coursename` varchar(250) DEFAULT NULL COMMENT '课程名称',
`STATUS` varchar(20) NOT NULL,
KEY `index1` (`student_number`) USING BTREE,
KEY `index2` (`starttime`) USING BTREE,
KEY `index3` (`coursename`) USING BTREE,
KEY `status` (`STATUS`) USING BTREE
) ENGINE=InnoDB DEFAULT CHARSET=utf8

给建好的表加一个自动增长的主键

alter table `表格名` add column `列名` int not null auto_increment primary key comment '主键' first;

错误的查询结果和错误的用法

SELECT
a.student_number AS student_number,
a.student_grade AS student_grade,
a.student_academy,
a.student_professional,
a.student_predictionclass AS student_predictionclass,
a.student_predictiongrade AS student_predictiongrade,
a.student_model_correlation_coefficient,
a.student_accuracy_model_points,
a.student_rate_return_model_exam,
a.student_false_alarm_rate_model_fail_exam,
a.student_model_training_sample,
b.average_grade AS average_grade,
e.xf
FROM
(student_gradeprediction a,
averager_grade b)
RIGHT OUTER JOIN (
SELECT
c.student_predictionclass,
c.xf
FROM
averager_grade d
RIGHT OUTER JOIN ( SELECT student_predictionclass, xf FROM studygrade, averager_grade WHERE student_predictionclass = kcmc ) c ON c.student_predictionclass = d.student_predictionclass
WHERE
c.xf IS NOT NULL
GROUP BY
c.student_predictionclass

) e ON e.student_predictionclass = a.student_predictionclass
WHERE
a.student_predictiongrade > 0
AND a.student_predictionclass = b.student_predictionclass
AND a.student_number = '2160400224'

%通配符

_通配符

正则表达式

虽然我对正则表达式还没具体的掌握，但是在今后的工作中一定要慢慢理解

Concat函数

Trim函数

常用算数运算符

函数

常用的日期处理函数

数值处理函数

聚合函数

AVG(),MAX(),MIN(),SUM(),COUNT(列名)这四个都是默认忽略NULL值得，而COUNT(*)就不会忽略NULL值

Distinct关键字

分组

子查询

组合查询