整理了日常用到的一些sqls
1.插入表
insert into table_B select * from table_A
2.清空表
truncate table test #清空表，结构还存在
delete table test where ... #删除表中特定的数据
drop table test #删除整表，包括结构
3. 导出到文件
select * from table_A where filed1 like '8422%' into outfile '/usr/local/mysql/8422.txt' fields terminated by '||'
4.导入文件到DB
LOAD DATA INFILE "/root/user/output.txt" INTO TABLE table_A CHARACTER SET gbk fields terminated by x'' IGNORE 1 LINES;
#字符集有时添加后会报错，可以去掉
5. 更新表
#一对一的情况
update table_A a, table_B b set a.field1 = b.field1 where a.field2 = b.field2 #一对多的情况
update table_A a inner join table_B b on a.route_id = b.valid_route_id set a.valid_route_id=b.valid_route_id
6. 字段拼接
UPDATE table_A set SIC_DESC=concat_ws('|',SICCODE1,SICCODE2,SICCODE3,SICCODE4)
7.字段截取
create table table_A ENGINE=MyISAM select locname,substring(file_name,1,3) from table_B where LOCNAME !=''
8.删除某列
alter table table_A drop column source_path
9.去重
table_A
+----+--------+
| id | name |
+----+--------+
| 1 | google |
| 2 | yahoo |
| 3 | msn |
| 4 | google |
| 5 | google |
| 6 | yahoo |
+----+--------+
#1 通过条件选取最大或最小的记录，来达到去重的目的
select * from table_A a where id=(select min(id) from table_A where name=a.name) #2 通过group by 和order by
select * from table_A group by name order by id desc; #3 keep the row with the lowest id
(1)DELETE n1 FROM table_A n1, table_A n2 WHERE n1.id > n2.id AND n1.name = n2.name
(2)DELETEFROM NAMES
WHERE id NOTIN(SELECT*FROM(SELECT MIN(n.id)FROM NAMES n
GROUPBY n.name) x) #4 keep the row with the highest id
DELETE n1 FROM names n1, names n2 WHERE n1.id < n2.id AND n1.name = n2.name
10.分组取最大的N条记录
#先添加一个rowid
select *from sh_20110401_bankup as T where 3>(select count(*) from sh_20110401_bankup
where field1=T.field1 and rowid>T.rowid order by T.field1,T.rowid desc )
11.分组取最大值
#通过两步
(1)create table sh_20110301_0331_ptp_t select record_date,substring(time_stamp,1,2)as tim,count(*)as cc from sh_20110301_0331_ptp
group by substring(time_stamp,1,2),record_date order by record_date,substring(time_stamp,1,2) (2)select * from sh_20110301_0331_ptp_t where cc in (select max(cc) from sh_20110301_0331_ptp_t
group by tim) order by tim
12.拆分分隔符
update table_A set custom11=substring_index(custom11,';',1)
13 日期转数字
update table_A set convert_date=unix_timestamp(record_date)
tt=TIME_TO_SEC(time_stamp)
14 MD5,字段不能有null
update table_A set dd = MD5(CONCAT_ws('$',id,attribute_key,attribute_value)
15 上一个月的数据
select * from review where period_diff(date_format(now() , '%Y%m') , date_format(`Review_Date`, '%Y%m')) =1;
16 上一周的数据
select Rating,count(*) from review where week(`Review_Date`)=7 group by Rating
17 最近7天的数据
select week(`Review_Date`) from review where date_sub(curdate(), INTERVAL 7 DAY) <= date(`Review_Date`)
18 字符变日期
update table_A set tt= str_to_date(date_created,'%m/%d/%Y')
19 字段拆分
update table_A set custom=substring_index(custom,';',1)