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MySQL 性能优化神器 Explain 使用分析

MySQL - EXPLAIN详解

1、时间比较

mysql> SELECT something FROM table　

WHERE TO_DAYS(NOW()) - TO_DAYS(date_col) <= 30;　

2、时间戳比较

select * from ds_order where order_state = 10 and (unix_timestamp(now()) - add_time)>600

3、在大数据的情况下，内连接是比外连接要快很多

join 处理出来13000左右，大概是7秒

left join == LEFT OUTER JOIN 处理出来23000左右，大概是49秒

4、mysql查最近的值，比如18查询最近的值，17，18，19

SELECT

*

FROM

(

SELECT DISTINCT

(user_id),

rob_prize

FROM

ds_purchase_record

WHERE

rob_prize <> 18

OR rob_prize = 18

ORDER BY

ABS(rob_prize-18) ASC

) AS one

GROUP BY

user_id

order by ABS(rob_prize-18) ASC;

5、用到and or

or 的写法要写()

select * from message where (typeid=31) or (typeid=30) or (typeid=32) or (typeid=33) order by id desc;

6、存储过程与创建函数的使用

存储过程与自定义函数的不同，存储过程可以返回多个字段，自定义函数只能返回一个字段

（1）存储过程：

# 删除过程

DROP PROCEDURE IF EXISTS getOrderInfo;

# 创建过程，只有IN的

delimiter //

CREATE PROCEDURE getOrderInfo(IN oid int(11))

BEGIN

select * from ds_order where order_id=oid;

END //

delimiter ;

call getOrderInfo(21);

# 删除过程

DROP PROCEDURE IF EXISTS getOrderField;

#创建过程，有IN（条件字段）的，也有OUT（输出字段）的

delimiter //

CREATE PROCEDURE getOrderField(IN oid int(11),OUT sn VARCHAR(255))

BEGIN

select order_sn INTO sn from ds_order where order_id=oid;

END //

delimiter ;

call getOrderField(21,@sn);

SELECT @sn;

# 删除过程

DROP PROCEDURE IF EXISTS getInfo;

delimiter //

CREATE PROCEDURE getInfo(IN oid int(11),IN dtable VARCHAR(25))

BEGIN

set @s = concat("select * from ",dtable," WHERE order_id = ",oid);

prepare stmt from @s; #预定义SQL

execute stmt; #填充SQL

DEALLOCATE prepare stmt; #

END //

delimiter;

call getInfo(21,'ds_order');

7、根据条件排序

SELECT

fg.*, a.uid,

a.if_boss,

CASE

WHEN (a.if_boss = 0 && uid = 179150) THEN

1

WHEN (a.if_boss is null) THEN

2

END AS num

FROM

ds_fight_group AS fg

LEFT JOIN ds_assemble AS a ON fg.fg_id = a.fg_id

ORDER BY

num ASC

SELECT

count(

CASE

WHEN da.if_boss = a.id THEN

1

ELSE

NULL

END

) as `_member`,

count(case when o.order_state>10 then 1 else null end) as `_order_count`,

a.uid,

a.id,

a.a_type

FROM

ds_assemble AS a

LEFT JOIN ds_assemble AS da ON da.if_boss = a.id

LEFT JOIN ds_order as o on o.order_sn=da.order_sn

WHERE

a.id > 0

AND a.if_boss = 0

GROUP BY

a.id

注意点：如果要判断null的话，这里要写 is null

SELECT

count(

CASE

WHEN da.if_boss = a.id THEN

1

ELSE

NULL

END

) AS fnum,

count(

CASE

WHEN o.order_state > 10 THEN

1

ELSE

NULL

END

) AS onum,

a.*, wx.avatar,

wx.mobile

FROM

ds_assemble AS a

LEFT JOIN ds_assemble AS da ON da.if_boss = a.id

LEFT JOIN ds_order AS o ON o.pay_sn = da.order_sn

LEFT JOIN ds_member AS m ON a.uid = m.member_id

LEFT JOIN ds_wxtempuser AS wx ON m.member_name = wx.mobile

LEFT JOIN ds_order AS orr ON a.order_sn = orr.pay_sn

WHERE

1 = 1

AND a.id > 0

AND a.if_boss = 0

AND a.fg_id = 7

AND (

a.add_time + 62400 > 1557133850

)

AND orr.order_state > 10

GROUP BY

a.id

HAVING

a.a_type > (onum + 1)

LIMIT 0,10

全部竞猜记录

SELECT

m.member_name,

gr.`name`,

gr.gj_id,

pr.rob_prize,

pr.addtime,

pr.pay_sn

FROM

ds_purchase_record AS pr

LEFT JOIN ds_member AS m ON pr.user_id = m.member_id

LEFT JOIN ds_grabjade AS gr ON pr.gid = gr.gj_id

ORDER BY

addtime DESC

根据一条纪录的维度查已售数量

SELECT

count(

CASE

WHEN da.if_boss = a.id THEN

1

ELSE

NULL

END

) AS fnum,

count(

CASE

WHEN da.a_status=1 && da.uid>0 THEN

1

ELSE

NULL

END

) AS onum,

a.*

FROM

ds_assemble AS a

LEFT JOIN ds_assemble AS da ON da.if_boss = a.id

WHERE

1 = 1

AND a.id > 0

AND a.if_boss = 0

AND a.fg_id = 16

and a.a_status=1

GROUP BY

a.id

这是保存的时间格式

<!-- 按日查询 -->   SELECT DATE_FORMAT(created_date,'%Y-%m-%d') as time,sum(money) money FROM o_finance_detail where org_id = 1000  GROUP BY  time   <!-- 按月查询 -->   SELECT DATE_FORMAT(created_date,'%Y-%m') as time,sum(money)  money FROM o_finance_detail where org_id = 1000  GROUP BY  time   <!-- 按年查询 -->   SELECT DATE_FORMAT(created_date,'%Y') as time,sum(money)  money FROM o_finance_detail where org_id = 1000  GROUP BY  time    <!-- 按周查询 -->   SELECT DATE_FORMAT(created_date,'%Y-%u') as time,sum(money)  money FROM o_finance_detail where org_id = 1000  GROUP BY  time

使用 FROM_UNIXTIME 可以把时间戳转换为日期：

select FROM_UNIXTIME(invest_time,'%Y年%m月%d') from crm_invest_apply

按指定排序

select * from fc_image where i_id in (50,42,58,41,43,44,60) ORDER BY field(i_id,50,42,58,41,43,44,60)

mysql也可以用IF来做判断

SELECT

age,

IF (

age = 10, // 条件

'你好', // 为true时的答案

'你不好' // 为false时的答案

) cn

FROM

fc_optimization

☐ HAVING cn = '你好' //最后的条件，不能用where去查条件，会报错