MySql 常用函数

1. replace(column,'old','new') 把column列中旧的数据替换成新的数据

update product set description=replace(description,'kindeditor','')

 

 2. LEFT(column, num) 查询column中Num个字节的字符串，用来查询子字符串

SELECT LEFT(NAME,2)  from city

 

 3. 查询当天数据 to_days()

mysql> select count(1) from flow_shipment where status=2 and  to_days(create_time)=to_days(now());

 

4. 查询一天前数据 date_sub（）

mysql> select count(1) from flow_shipment where status=2 and  create_time>DATE_SUB(CURDATE(), INTERVAL 1 DAY);

 

5. 查询30分钟前的数据 

select Id,OrderId,Status from OrderHistory where UpdateTime<(CURRENT_TIMESTAMP - INTERVAL 30 MINUTE)

 

 6. 查询前一天的数据 to_days()

select * from order_info where TO_DAYS(NOW())-TO_DAYS(order_time) = 1 

 

7. 查询当月数据

SELECT * FROM order_info WHERE DATE_FORMAT(order_time, '%Y%m') = DATE_FORMAT(CURDATE(), '%Y%m')

 

 8. 删除重复数据，只留一条

delete from order_info
where id not in (
 select max(id) from order_info group by order_id order by order_id)

 

 9. 删除表中多余的重复记录（多个字段），数据库只保留id最大的记录

delete from order_detail where id in(
select a.id from (
select id from order_detail 
where (order_id,sku_id) in (select order_id,sku_id from order_detail
group by order_id,sku_id having count(*) > 1)
and id not in (select max(id) from order_detail group by order_id,sku_id having count(*)>1)
) a
)