Question

为什么这个查询：

SELECT inv.batch_number_id AS batch_number_id,
   inv.expiry_date AS expiry_date,
   inv.facility_id AS facility_id,
   inv.id AS id,
   fac.code AS facility_code,
   inv_st.description AS status,
   bn.batch_nbr AS batch_number,
   bn.expiry_date AS batch_expiry_date,
   sum(CASE WHEN al.status_id < 90 THEN al.alloc_qty ELSE 0 END) AS alloc_qty
FROM inventory inv
INNER JOIN facility fac ON inv.facility_id = fac.id
INNER JOIN inventory_status inv_st ON inv.status_id = inv_st.id
LEFT OUTER JOIN batch_number bn ON inv.batch_number_id = bn.id
LEFT OUTER JOIN allocation al ON al.from_inventory_id = inv.id
GROUP BY inv.id,
     facility_code,
     status,
     batch_number,
     batch_expiry_date

在postgres 9.1.6工作？

从文档：＆＃34;当存在GROUP BY时，SELECT列表表达式无法引用除聚合函数之外的未组合列，因为对于未组合的列表，将返回多个可能的值。柱＆＃34;

如果我将fac.id添加到select表达式中，我会得到预期的＆＃34; ERROR：列＆＃34; fac.id＆＃34;必须出现在GROUP BY子句中或用于聚合函数＆＃34;。为什么postgres抱怨该列而忽略了facility_id？（在原始查询中还有很多其他列也以同样的方式违反了我的期望。为了清晰起见，缩短了示例。）

Answer 1

The whole quote is：

当存在GROUP BY时，SELECT列表表达式无法引用未聚合的列，但聚合函数内或未分组的列在功能上依赖于分组列，因为它会否则为一个未分组的列返回多个可能的值。 如果分组列（或其子集）是包含未分组列的表的主键，则存在功能依赖性。

更新：此功能已添加到9.1

中

为什么Postgres允许我让列不在Group By中？

1 个答案: