Question

 WHERE (ADDR1 = '1500 Valley Rd' AND CUST_FLAG = 'P')     -- 1
    OR (ADDR1 = '1500 Valley Rd' AND CUST_FLAG = 'J')     -- 2

请帮我解决这条问题。我只需要显示CUST_FLAG = 'P'的记录。使用上面的Where子句，如果两个条件都满足，我将获得两个记录。我的要求是：

如果只满足第一个条件，则返回记录CUST_FLAG = 'P'
如果只满足第二个条件，则返回记录CUST_FLAG = 'J'
如果两个条件都满足，则仅返回带有CUST_FLAG = 'P'的记录。

Answer 1

这是优先级查询。要在单个where子句中执行此操作，您可以执行以下操作：

WHERE ADDR1 = '1500 Valley Rd' AND
      (CUST_FLAG = 'P' OR
       (CUST_FLAG = 'J' AND
        NOT EXISTS (SELECT 1 FROM t WHERE t.ADDR1 = outer.ADDR1 AND t.CUST_FLAG = 'J'
       ))

或者更典型的方法是使用ROW_NUMBER()：

select t.*
from (select t.*, row_number() over (partition by addr1 order by cust_flag desc) as seqnum
      from (<your query here>) t
     ) t
where seqnum = 1;

Answer 2

尝试玩case/when

case 
  when ADDR1 = '1500 Valley Rd' AND CUST_FLAG = 'P' then 'P'
  when ADDR1 = '1500 Valley Rd' AND CUST_FLAG = 'J' then 'J'
  else 'P' end

Answer 3

您可以通过对记录进行排序并仅获取第一个记录来实现此目的。（但请注意，ROWNUM可能是特定于Oracle的语法。）

SELECT * FROM (
SELECT <column_list> 
FROM <table>
WHERE ((ADDR1 = '1500 Valley Rd' AND CUST_FLAG = 'P')     -- 1
    OR (ADDR1 = '1500 Valley Rd' AND CUST_FLAG = 'J'))     -- 2
ORDER BY CUST_FLAG DESC
) WHERE ROWNUM = 1

自Oracle 12c以来，还可以使用以下语法：

SELECT <column_list> 
FROM <table>
WHERE ((ADDR1 = '1500 Valley Rd' AND CUST_FLAG = 'P')     -- 1
    OR (ADDR1 = '1500 Valley Rd' AND CUST_FLAG = 'J'))     -- 2
ORDER BY CUST_FLAG DESC
FETCH FIRST 1 ROWS ONLY;

另见： - On ROWNUM and Limiting Results - How do I limit the number of rows returned by an Oracle query after ordering?

SQL Query仅返回1条记录，满足2个条件

3 个答案: