PostgreSQL 递归查询一例 - 资金累加链

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背景

云栖社区问答中,一位网友的问题:

one等于上一个one加上现在的money,如何填充one字段?语句怎么写?

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解法

在PostgreSQL中,可以使用递归查询满足以上业务场景的需求:

需要用到递归查询。

postgres=# create table m(id serial primary key,money int, one int);  
CREATE TABLE  
postgres=# insert into m(money,one) values (0,2000),(85,0),(100,0),(19,0),(21,0);  
INSERT 0 5  
postgres=# select * from m;  
 id | money | one    
----+-------+------  
  1 |     0 | 2000  
  2 |    85 |    0  
  3 |   100 |    0  
  4 |    19 |    0  
  5 |    21 |    0  
(5 rows)  
  
postgres=# with recursive t(id,money,one) as (select 1 id,0 money,2000 one union all select t1.id,t1.money,t.one-t1.money one from t,m t1 where t.id=t1.id-1) select * from t;  
 id | money | one    
----+-------+------  
  1 |     0 | 2000  
  2 |    85 | 1915  
  3 |   100 | 1815  
  4 |    19 | 1796  
  5 |    21 | 1775  
(5 rows)  

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