Question

我有一张这样的表

AMID     Entry
------- ---------
1000     MARS
1001     JUPITER
1002     SATURN
1003     VENUS
1003     SATURN
1004     NEPTUNE
1004     SATURN
1005     JUPITER
1005     MARS

现在我想用特定的ENTRY值提取DISTINCT AMID值。结束表应该是这样的

 AMID     Entry
-------- --------
  1000    MARS
  1001    JUPITER
  1002    SATURN
  1003    VENUS
  1004    SATURN
  1005    MARS

选择ENTRY值的条件是，

必须根据此优先级获取值：

VENUS

MARS

JUPITER

SATURN

NEPTUNE

因此，如果任何AMID同时具有VENUS和MARS，则应该使用VENUS
MARS和SATURN，它应该采取MARS
NEPTUNE和JUPITER，它应该采用JUPITER。（按优先级选择）。

Answer 1

您可以使用排名功能（如果您使用的是SQL Server 2008）：

DECLARE @t TABLE (AMID INT, Entry VARCHAR(100))
INSERT @t 
VALUES
(       1000                   ,'MARS'),
(       1001                   ,'JUPITER'),
(       1002                   ,'SATURN'),
(       1003                   ,'VENUS'),
(       1003                   ,'SATURN'),
(       1004                   ,'NEPTUNE'),
(       1004                   ,'SATURN'),
(       1005                   ,'JUPITER'),
(       1005                   ,'MARS')

;WITH a AS(
    SELECT  *,
            ROW_NUMBER() OVER (PARTITION BY AMID ORDER BY 
                CASE Entry 
                    WHEN 'VENUS' THEN 0
                    WHEN 'MARS' THEN 1
                    WHEN 'JUPITER' THEN 2
                    WHEN 'SATURN' THEN 3
                    WHEN 'NEPTUNE' THEN 4
                END) num
    FROM    @t
)

SELECT  AMID, Entry
FROM    a
WHERE   num = 1

Answer 2

试试这个：

;WITH CTE AS (
SELECT *,ROW_NUMBER() OVER(PARTITION BY AMID ORDER BY T.PRIORITY) AS ROWNUM
FROM PLANETS P
JOIN
    (
    SELECT 1 PRIORITY, 'VENUS' AS NAME UNION ALL
    SELECT 2, 'MARS'  UNION ALL
    SELECT 3, 'JUPITER'  UNION ALL
    SELECT 4, 'SATURN'  UNION ALL
    SELECT 5, 'NEPTUNE')T
ON T.NAME=P.[ENTRY]
)SELECT AMID,[ENTRY] FROM CTE WHERE ROWNUM=1

SQL Fiddle demo

Answer 3

尝试这个MySQL查询：

SELECT AMID, (CASE MIN(Entry) WHEN 1 THEN "VENUS"
                              WHEN 2 THEN "MARS"
                              WHEN 3 THEN "JUPITER"
                              WHEN 4 THEN "SATURN"
                              WHEN 5 THEN "NEPTUNE"
              END) AS Entry
FROM (
       SELECT AMID, (CASE Entry WHEN "VENUS" THEN 1
                                WHEN "MARS" THEN 2
                                WHEN "JUPITER" THEN 3
                                WHEN "SATURN" THEN 4
                                WHEN "NEPTUNE" THEN 5
                     END) AS Entry
       FROM table_name
      ) a
GROUP BY AMID;

Answer 4

为什么不直接将条目值放在自己的表中：

CREATE TABLE entry_value
(
    entry VARCHAR(10) NOT NULL PRIMARY KEY,
    value INT NOT NULL
);

INSERT INTO entry_value VALUES
    ('VENUS', 0),
    ('MARS', 1),
    ('JUPITER', 2),
    ('SATURN', 3),
    ('NEPTUNE', 4)    
;

然后找到你想要的东西是微不足道的：

SELECT
    a.amid,
    (SELECT entry FROM entry_value where value = MIN(e.value)) AS entry
FROM amid a
JOIN entry_value e
ON e.entry = a.entry
GROUP BY a.amid
ORDER BY a.amid;

作为一个额外的好处，你可以在输入栏中添加一个外键，这样人们就不会把1000, 'PLUTO'之类的垃圾放在那里。

根据优先级从列中选择值

4 个答案: