postgresql行转列

Posted 2021-01-01 吃饭睡觉打逗逗

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,
split_part(split_part(temp,\',\',2),\':\',2) as 身高,
split_part(split_part(temp,\',\',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, string_agg(zbfm||\':\'||value,\',\') 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, zbfm, value) values\'
        for j in range(100):
            for name in names:
                for zbfm in zbfms:
                    sqlstr += "(\'%s\',\'%s\',%d),"%(name+str(i*100+j),zbfm,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