SQL-如果满足特定条件，则从表中进行SELECT，否则满足条件

Question

如何在SQL中执行此操作：

1. SELECT CLIENT, PAYMENT_CODE FROM PAYMENTS_TABLE
2. If PAYMENT_CODE = 1, SELECT other data from table_1
3. Else, SELECT other data from table_2

我想要的结果是：

| Client | Payment Code = 1 | Address from table_1 | Phone from table_1 | ...

要么

| Client | Payment Code  1 | Address from table_2 | Phone from table_2 | ...

提前致谢！

Answer 1

尽管Rajesh的解决方案很好，但是您也可以使用两个LEFT JOIN来完成；

SELECT pt.CLIENT, pt.PAYMENT_CODE, 
       COALESCE(t1.address, t2.address) address, 
       COALESCE(t1.phone,   t2.Phone)   phone
FROM PAYMENTS_TABLE pt
LEFT JOIN Table_1 t1 
  ON pt.client_code = t1.client_code AND pt.PAYMENT_CODE =  1
LEFT JOIN Table_2 t2 
  ON pt.client_code = t2.client_code AND pt.PAYMENT_CODE <> 1

编辑：根据对另一个答案的评论，添加了client_code作为链接条件。

Answer 2

您需要使用UNION ，当payment_code = 1时，一个SELECT查询可从表_1获取详细信息，而另一个SELECT ，如果payment_code不等于1，则可从表_2获取详细信息

SELECT CLIENT, PAYMENT_CODE, T1.Address, T1.Phone FROM PAYMENTS_TABLE
JOIN Table_1 T1
ON -- your condition
WHERE PAYMENT_CODE =1
UNION 
SELECT CLIENT, PAYMENT_CODE, T2.Address, T2.Phone FROM PAYMENTS_TABLE
JOIN Table_2 T2
ON -- your condition
WHERE PAYMENT_CODE <> 1

Answer 3

您没有告诉我们table_1和table_2如何链接到payments_table，但是这样的方法应该起作用：

select p.client, 
       p.payment_code,
       case 
          when payment_code = 1 then t1.address
          else t2.address
       end as address,
       case 
          when payment_code = 1 then t1.phone
          else t2.phone
       end as phon
from payments_table p
   left join table_1 t1 on p.some_column = t1.some_column
   left join table_2 t2 on p.some_column = t2.come_column