sql - postgresql中选择查询的划分

Question

下面给出了我的表

create table batches ( batchid int,free smallint,qty int)


INSERT INTO batches VALUES (2329, 0, 100);
INSERT INTO batches VALUES (2329, 1, 10);
INSERT INTO batches VALUES (2331, 0, 75);
INSERT INTO batches VALUES (2331, 1, 4);

这个表会返回

 batchid free qty 
 2329    0    100
 2329    1    10
 2331    0    75
 2331    1    4

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需要对 列 qty
执行除法，即在这种情况下，100 应该除以 10(batchid应该相同)100/10(这里的 10 是 qty，其中 free = 1)

预期结果

Batchid  freelimit
2329     10
2331     18

Answer 1

WITH Queries (Common Table Expressions)

with a as (
    select 
      batchid,qty 
    from batches  
    where  free = 0 order by batchid 
)
, b as (
    select 
      batchid,qty 
    from batches  
    where  free = 1order by batchid 
)
select 
  batchid, floor((a.qty/b.qty))::real as freelimit 
from a inner join b using(batchid)

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SQLFIDDLE-DEMO