SQL 结果中带有额外不常见字段的联合查询

Question

我有四个 table，现在我使用 UNION sql 查询显示四个公共字段。

问题：我想显示一个不常见的字段（公司），在 table 中名称为 Multiple Product with current result.How 我可以这样做吗？

当前 SQL :

SELECT * 
FROM ( SELECT reference_number,name,contact_no,email,create_date,'Credit Card' AS card_type 
       FROM credit_card 
       UNION 
       SELECT reference_number,name,contact_no,email,create_date,'Personal Loan' AS card_type 
       FROM personal_loan
       UNION 
       SELECT reference_number,name,contact_no,email,create_date,'Financial Health' AS card_type
       FROM financial_health
       UNION
       SELECT reference_number,name,contact_no,email,create_date,'Multiple Product' AS card_type
       FROM multiple_products ) A

Answer 1

您可以向 space 中您想要 return Company 的其他 SELECT 查询添加一个空（或 NULL）字段] 字段。

SELECT * 
FROM ( SELECT reference_number,
              name,
              contact_no,
              email,
              create_date,
              'Credit Card' AS card_type,
              '' AS company -- use NULL here if you prefer
       FROM credit_card 
       UNION 
       SELECT reference_number,name,contact_no,email,create_date,'Personal Loan' , ''
       FROM personal_loan
       UNION 
       SELECT reference_number,name,contact_no,email,create_date,'Financial Health' , ''
       FROM financial_health
       UNION
       SELECT reference_number,name,contact_no,email,create_date,'Multiple Product' , Company
       FROM multiple_products ) A

请注意，您只需要第一个 SELECT 的列别名。

SQL 结果中带有额外不常见字段的联合查询

SQL UNION Query with Extra uncommon Field in Results

sql

union