如何在 SQL 中将多行合并为一行？

Question

我有一个包含以下列的特定表格 -

属性 ID 可以有 6 个可能的值，从 1 到 6。此表将包含所有客户的条目。客户的每一行都包含 1-6 个值的条目。

现在我想要实现的目标如下 -

我执行以下查询 -

SELECT CUST_ID,
        CASE WHEN "ATTR ID"=1 THEN "ATTR_VALUE" END AS ATTR_ID_1,
        CASE WHEN "ATTR ID"=2 THEN "ATTR_VALUE" END AS ATTR_ID_2,
        CASE WHEN "ATTR ID"=3 THEN "ATTR_VALUE" END AS ATTR_ID_3,
        CASE WHEN "ATTR ID"=4 THEN "ATTR_VALUE" END AS ATTR_ID_4,
        CASE WHEN "ATTR ID"=6 THEN "ATTR_VALUE" END AS ATTR_ID_5,
        CASE WHEN "ATTR ID"=7 THEN "ATTR_VALUE" END AS ATTR_ID_6
        
FROM "TABLE_NAME" where CUST_ID='20002123'

这会很好地产生 6 列，但最终也会创建 3 行 -

我应该旋转表格吗？

谢谢

Answer 1

你很接近：

SELECT CUST_ID,
    max(CASE WHEN "ATTR ID"=1 THEN "ATTR_VALUE" END) AS ATTR_ID_1,
    max(CASE WHEN "ATTR ID"=2 THEN "ATTR_VALUE" END) AS ATTR_ID_2,
    max(CASE WHEN "ATTR ID"=3 THEN "ATTR_VALUE" END) AS ATTR_ID_3,
    max(CASE WHEN "ATTR ID"=4 THEN "ATTR_VALUE" END) AS ATTR_ID_4,
    max(CASE WHEN "ATTR ID"=6 THEN "ATTR_VALUE" END) AS ATTR_ID_5,
    max(CASE WHEN "ATTR ID"=7 THEN "ATTR_VALUE" END) AS ATTR_ID_6

FROM "TABLE_NAME" where CUST_ID='20002123'
Group by cust_id;

另外，您可以查看枢轴。

Answer 2

您可以使用GROUP BY CUST_ID 聚合以将多行作为单行。

尝试如下更改您的查询。

SELECT CUST_ID, 
       Max(ATTR_ID_1) AS ATTR_ID_1, 
       Max(ATTR_ID_2) AS ATTR_ID_2, 
       Max(ATTR_ID_3) AS ATTR_ID_3, 
       Max(ATTR_ID_4) AS ATTR_ID_4, 
       Max(ATTR_ID_5) AS ATTR_ID_5, 
       Max(ATTR_ID_6) AS ATTR_ID_6 
FROM   (SELECT CUST_ID, 
               CASE WHEN "ATTR ID" = 1 THEN "ATTR_VALUE"  END AS ATTR_ID_1, 
               CASE WHEN "ATTR ID" = 2 THEN "ATTR_VALUE"  END AS ATTR_ID_2, 
               CASE WHEN "ATTR ID" = 3 THEN "ATTR_VALUE"  END AS ATTR_ID_3, 
               CASE WHEN "ATTR ID" = 4 THEN "ATTR_VALUE"  END AS ATTR_ID_4, 
               CASE WHEN "ATTR ID" = 6 THEN "ATTR_VALUE"  END AS ATTR_ID_5, 
               CASE WHEN "ATTR ID" = 7 THEN "ATTR_VALUE"  END AS ATTR_ID_6 
        FROM   "TABLE_NAME" 
        WHERE  CUST_ID = '20002123')T 
GROUP  BY CUST_ID