日常收集整理常见的mysql sql技巧

编程学习 2021-07-05 15:28www.dzhlxh.cn编程入门
本篇内容是长沙网络推广日常收集整理常见的mysql sql技巧,对大家学习mysql sql技巧相关内容有所帮助,感兴趣的朋友一起学习吧

废话不多说了,直接给大家贴代码了。

1,数字辅助表

//创建表
create table test(id int unsigned not null primary key);
delimiter //
create procedure pnum(cnt int unsigned)
begin
declare i int unsigned default 1;
insert into num select i;
while i*2 < cnt do
insert into num select i+id from num ;
set i=i*2;
end while;
end
//
delimiter ;
#####列值不连续问题:
表a中id值为1,2,3,100,101,110,111
set @q=0;
select id,@q:=@q+1 as cn from a;
#####对不连续的进行分组
set @a=0;
select min(id) as start_v,max(id) as end_v from (
select id,cn,id-cn as diff from (
select id,@a:=@a+1 as cn from pi) as p ) as pp group by diff;
#####对不连续的值填充
use test;
DROP TABLE if EXISTS pincer;
create table pincer(a int UNSIGNED);
insert into pincer values(1),(2),(5),(100),(101),(103),(104),(105);
select a+1 as start ,(select min(a)-1 from pincer as ww where ww.a>qq.a) as end from pincer as qq where 
not exists (select * from pincer as pp where qq.a+1=pp.a)
and a<(select max(a) from pincer);
################
select id,num,ranknum,diff from (select id,num,ranknum,num-ranknum as diff from (select id,num,if(@id=id,@rownum:=@rownum+1,@rownum:=1) ranknum,@id:=id from tt,(select @rownum:=0,@id:=null) a ) b) c group by id,diff having count(*)>=2;
################

2,生日问题

select name,birthday,if(cur>today,cur,next) as birth_day
from(
select name,birthday,today,date_add(cur,interval if(day(birthday)=29 && day(cur)=28,1,0) day)as cur, date_ad(next,interval if(day(birthday)=29 && day(next)=28,1,0) day) as next
from(
select name,birthday,today,
  date_add(birthday,interval diff year) as cur,
  date_add(birthday,interval diff+1 year) as next,
from(
select concat(laster_name,'',first_name) as name,
  birth_date as birthday,
  (year(now())-year(birth_date) )as diff,
  now() as today
  from employees) as a
) as b
) as c

3,日期问题----计算工作日

create table sals(id int ,date datetime ,cost int,primary key(id);
select date_add('1900-01-01',
            interval floor(datediff(date,'1900-01-01')/7)*7 day)
            as week_start,
            date_add('1900-01-01',
            interval floor(datediff(date,'1900-01-01')/7*7+6 day)
            as week_end,
            sum(cost) from sales;
计算工作日(指定2个日期段 有多少工作日)
create procedure pgetworkdays (s datetime,e datetime)
begin
select floor(days/7)*5+days%7
case when 6 between wd and wd+days%7-1 then 1 else 0 end
case then 7 between wd and wd+days%7-1 then 1 else 0 end
from 
(select datediff(e,s)+1 as days,weekday(s)+1 as wd) as a;
end;

mysql sql语句大全

1、说明:创建数据库
CREATE DATABASE database-name

2、说明:删除数据库

drop database dbname

3、说明:备份sql server
--- 创建 备份数据的 device
USE master
EXEC sp_addumpdevice 'disk', 'testBack', 'c:\mssql7backup\MyNwind_1.dat'
--- 开始 备份
BACKUP DATABASE pubs TO testBack

4、说明:创建新表

create table tabname(col1 type1 [not null] [primary key],col2 type2 [not null],..)
根据已有的表创建新表:
A:create table tab_new like tab_old (使用旧表创建新表)
B:create table tab_new as select col1,col2… from tab_old definition only

5、说明:删除新表

drop table tabname

6、说明:增加一个列
Alter table tabname add column col type
注:列增加后将不能删除。DB2中列加上后数据类型也不能改变,唯一能改变的是增加varchar类型的长度。

7、说明:添加主键: Alter table tabname add primary key(col)
说明:删除主键: Alter table tabname drop primary key(col)

8、说明:创建索引:create [unique] index idxname on tabname(col….)

删除索引:drop index idxname

注:索引是不可更改的,想更改必须删除重新建。

9、说明:创建视图:create view viewname as select statement

删除视图:drop view viewname

10、说明:几个简单的基本的sql语句
选择:select * from table1 where 范围
插入:insert into table1(field1,field2) values(value1,value2)
删除:delete from table1 where 范围
更新:update table1 set field1=value1 where 范围
查找:select * from table1 where field1 like '%value1%' ---like的语法很精妙,查资料!
排序:select * from table1 order by field1,field2 [desc]
总数:select count as totalcount from table1
求和:select sum(field1) as sumvalue from table1
平均:select avg(field1) as avgvalue from table1
最大:select max(field1) as maxvalue from table1
最小:select min(field1) as minvalue from table1

11、说明:几个高级查询运算词
A: UNION 运算符
UNION 运算符通过组合其他两个结果表(例如 TABLE1 和 TABLE2)并消去表中任何重复行而派生出一个结果表。当 ALL 随 UNION 一起使用时(即 UNION ALL),不消除重复行。两种情况下,派生表的每一行不是来自 TABLE1 就是来自 TABLE2。
B: EXCEPT 运算符
EXCEPT 运算符通过包括所有在 TABLE1 中但不在 TABLE2 中的行并消除所有重复行而派生出一个结果表。当 ALL 随 EXCEPT 一起使用时 (EXCEPT ALL),不消除重复行。
C: INTERSECT 运算符
INTERSECT 运算符通过只包括 TABLE1 和 TABLE2 中都有的行并消除所有重复行而派生出一个结果表。当 ALL 随 INTERSECT 一起使用时 (INTERSECT ALL),不消除重复行。
注:使用运算词的几个查询结果行必须是一致的。

12、说明:使用外连接

A、left (outer) join:
左外连接(左连接):结果集几包括连接表的匹配行,也包括左连接表的所有行。
SQL: select a.a, a.b, a.c, b.c, b.d, b.f from a LEFT OUT JOIN b ON a.a = b.c
B:right (outer) join:
右外连接(右连接):结果集既包括连接表的匹配连接行,也包括右连接表的所有行。
C:full/cross (outer) join:
全外连接:不仅包括符号连接表的匹配行,还包括两个连接表中的所有记录。
12、分组:Group by:
  一张表,一旦分组完成后,查询后只能得到组相关的信息。
 组相关的信息:(统计信息) count,sum,max,min,avg  分组的标准)
    在SQLServer中分组时:不能以text,ntext,image类型的字段作为分组依据
 在selecte统计函数中的字段,不能和普通的字段放在一起;

13、对数据库进行操作:

分离数据库: sp_detach_db; 附加数据库:sp_attach_db 后接表明,附加需要完整的路径名

14.如何修改数据库的名称:

sp_renamedb 'old_name', 'new_name'

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