Question

在Postgresql 9.1+中我试图使用ROW_NUMBER（）别名字段过滤WHERE子句中的结果集。此查询工作正常：

SELECT inv.client_pk, 
       inv.invoice_pk, inv.contract_pk, 
       ROW_NUMBER() OVER ( PARTITION BY inv.client_pk ORDER BY inv.client_pk) as row_number 
FROM controllr.client as cli 
  LEFT JOIN controllr.invoice as inv ON inv.client_pk = cli.client_pk                              
WHERE client_status != 3;

但是当我在WHERE中添加“row_number”时：

SELECT inv.client_pk, 
       inv.invoice_pk, inv.contract_pk, 
       ROW_NUMBER() OVER ( PARTITION BY inv.client_pk ORDER BY inv.client_pk) as row_number 
FROM controllr.client as cli 
  LEFT JOIN controllr.invoice as inv ON inv.client_pk = cli.client_pk                              
WHERE client_status != 3 
  AND row_number <= 3;

它给了我一个错误：

列“row_number”不存在

当字段“row_number”明显作为别名字段存在时。

我做错了什么？

ps：我已经尝试过HAVING子句

Answer 1

使用子查询：

SELECT 
    *
FROM
    (SELECT 
         inv.client_pk, inv.invoice_pk, inv.contract_pk, 
         ROW_NUMBER() OVER (PARTITION BY inv.client_pk ORDER BY inv.client_pk) AS row_number 
     FROM 
         controllr.client as cli 
     LEFT JOIN 
         controllr.invoice as inv ON inv.client_pk = cli.client_pk                              
     WHERE 
         client_status != 3) AS sub
WHERE 
    row_number <= 3;

使用CTE：

WITH cte AS 
(
    SELECT 
        inv.client_pk, inv.invoice_pk, inv.contract_pk, 
        ROW_NUMBER() OVER ( PARTITION BY inv.client_pk ORDER BY inv.client_pk) AS row_number 
    FROM 
        controllr.client as cli 
    LEFT JOIN 
        controllr.invoice as inv ON inv.client_pk = cli.client_pk                              
    WHERE 
        client_status != 3
)
SELECT *
FROM cte
WHERE row_number <= 3;

您收到该错误的原因是因为在WHERE子句之前处理了SELECT子句。因此，在尝试使用原始查询处理条件row_number时，引擎无法将... row_number <= 3视为列。

此外，使用CTE与使用子查询具有相同的性能，但它确实提高了可读性。

Answer 2

使用子查询：

SELECT client_pk, invoice_pk, contract_pk
FROM
(
SELECT inv.client_pk, inv.invoice_pk, inv.contract_pk,
                     ROW_NUMBER() OVER
           ( PARTITION BY inv.client_pk
                      ORDER BY inv.client_pk) as row_number
FROM  controllr.client as cli 
LEFT JOIN  controllr.invoice as inv ON inv.client_pk = cli.client_pk 

WHERE client_status !=3  
) t                            
     WHERE row_number <= 3;

在WHERE中使用ROW_NUMBER（）别名

2 个答案: