在选择查询中添加 ORDER BY 时出错答案

【问题标题】：Error when adding ORDER BY in Select Query在选择查询中添加 ORDER BY 时出错
【发布时间】：2014-09-26 05:26:21
【问题描述】：

select 
    distinct on (productid)p.product,
    pb.productid, 
    pb.mrp,
    pb.ptr,
    pb.ssr,
    pt.patent
from  prod_batch pb
    inner Join  prod_patent pt using(patentid) 
    inner Join  prods p using(productid)  
where(qty - iqty) > 0

此选择正确返回并得到我真正想要的。！
当在上面添加ORDER BY 时选择根据product 的名称进行排序
我以前是这样写的。。

select 
    distinct on (productid)p.product,
    pb.productid, 
    pb.mrp,
    pb.ptr,
    pb.ssr,
    pt.patent
from  prod_batch pb
    inner Join  prod_patent pt using(patentid) 
    inner Join  prods p using(productid)  
where(qty - iqty) > 0 
order by 
    product -- this is my column name to order by

执行此操作时出错

错误：SELECT DISTINCT ON 表达式必须匹配初始 ORDER BY 表达式

【问题讨论】：

标签： sql postgresql sql-order-by distinct

【解决方案1】：

你可以这样试试

选择 - 1

select * from (
select 
    distinct on (productid)p.product,
    pb.productid, 
    pb.mrp,
    pb.ptr,
    pb.ssr,
    pt.patent
from  prod_batch pb
    inner Join  prod_patent pt using(patentid) 
    inner Join  prods p using(productid)  
where(qty - iqty) > 0 
order by 
    product
) t order by product

选择 - 2

With cte as (
select 
        distinct on (productid)p.product,
        pb.productid, 
        pb.mrp,
        pb.ptr,
        pb.ssr,
        pt.patent
    from  prod_batch pb
        inner Join  prod_patent pt using(patentid) 
        inner Join  prods p using(productid)  
    where(qty - iqty) > 0 

) select * from cte order by product

选择 - 3

只需将您的选择放入视图中

create or replace view pro_details as 
select 
    distinct on (productid)p.product,
    pb.productid, 
    pb.mrp,
    pb.ptr,
    pb.ssr,
    pt.patent
from  prod_batch pb
    inner Join  prod_patent pt using(patentid) 
    inner Join  prods p using(productid)  
where(qty - iqty) > 0

用法：select * from pro_details order by product

【讨论】：

选择选项 3

【解决方案2】：

DISTINCT ON (表达式 [, ...] ) 仅保留给定表达式计算结果为相等的每组行的第一行。 [...] 请注意，除非使用 ORDER BY 来确保所需的行首先出现，否则每组的“第一行”是不可预测的。 [...] DISTINCT ON 表达式必须匹配最左边的 ORDER BY 表达式。

尝试关注

select 
     distinct on (productid)p.product,
     pb.productid, 
     pb.mrp,
     pb.ptr,
     pb.ssr,
     pt.patent
from  prod_batch pb
inner Join  prod_patent pt using(patentid) 
inner Join  prods p using(productid)  
where(qty - iqty) > 0 
order by 
     p.productid,p.product

【讨论】：

【解决方案3】：

add table aliase with field "product"

select 
    distinct on (productid)p.product,
    pb.productid, 
    pb.mrp,
    pb.ptr,
    pb.ssr,
    pt.patent
from  prod_batch pb
    inner Join  prod_patent pt using(patentid) 
    inner Join  prods p using(productid)  
where(qty - iqty) > 0 
order by 
    p.product

【讨论】：