postgresql行专列

问：怎么分页&&按条件&&按顺序&&姓名不重复查出数据？

答：其实就是行转列，那么，postgresql怎么进行转列呢，百度了下，大概有三种写法

 

写法1 

group by + sum + case when

select name,sum(case when zbfm=‘年龄‘ then value else 0 end) as 年龄,sum(case when zbfm=‘身高‘ then value else 0 end) as 身高,sum(case when zbfm=‘体重‘ then value else 0 end) as 体重
from test group by name
having name like ‘%1‘ and length(name)=4 order by 年龄 desc

 

写法2

用postgresql的crosstab交叉函数

crosstab(unknown,unknown) does not exist

select * from
crosstab(
‘select name,zbfm,value from test where name like ‘‘%1‘‘ and length(name)=4‘,$$values(‘年龄‘),(‘身高‘),(‘体重‘)$$)
as score(name text,年龄 int,身高 int,体重 int)
order by 年龄 desc

 

写法3

group by + string_agg + split_part(分组，行转列，字符切割)

select name,split_part(split_part(temp,‘,‘,1),‘:‘,2) as 年龄,2),2) as 身高,3),2) as 体重
from(
select name,string_agg(zbfm||‘:‘||value,‘,‘) as temp from test
group by name 
having name like ‘%1‘ and length(name)=4
) as t order by 年龄 desc

group by + string_agg

select name,‘) from test
group by name 
having name like ‘%1‘ and length(name)=4

 

其他

建表语句

CREATE TABLE test
(
  id serial NOT NULL,value integer,name character varying,zbfm character varying,CONSTRAINT pkey PRIMARY KEY (id)
)

插入数据(python)

import psycopg2
from random import random
conn = psycopg2.connect(database="postgres",user="postgres",password="password",host="ip",port="port")
cur = conn.cursor()

def insertData():
    names = [‘路人甲‘,‘王尼玛‘,‘唐马儒‘]
    zbfms = [‘年龄‘,‘身高‘,‘体重‘]

    for i in range(100):
        sqlstr = ‘insert into test(name,value) values‘
        for j in range(100):
            for name in names:
                for zbfm in zbfms:
                    sqlstr += "(‘%s‘,‘%s‘,%d),"%(name+str(i*100+j),int(100*random()))
        cur.execute(sqlstr[:-1])
        conn.commit()
        print(i)

if __name__ == ‘__main__‘:
    insertData()
    selectData()

 

 

参考

PostgreSQL 实现交叉表（行列转换）的五种方法