Question

我有这张桌子：

select * from scott.test;

a   b   c
---------
26  R   4
26  T   5
26  S   2
25  Y   2
25  U   3
24  X   3
22  Z   3
21  P   3

我需要的是：对于给定的“a”，我必须提取所有细节（a，b，c），如果有多于一个“a”，我想只提取具有最高“c”的那个。例如，对于26，我只想提取：

a  b  c
26 T  5

我这样做了：

select * from scott.test where a = 26 and c = (select max(c) from scott.test where a = 26);

但我只需要一个选择（不在select中选择）。可以吗？谢谢！

Answer 1

使用 ROW_NUMBER（）分析功能，您可以实现它。但是，您需要使用子查询来完成此操作。但是你总是可以使用 WITH 子句来区分它。

以下查询会提示您输入列a的值，并返回最大值为c的行。 WITH子句的第一部分仅用于构建示例的示例数据，您只需要第二部分，即t。

例如，

输入a的值26：

SQL> WITH data AS
  2    (SELECT 26 AS a, 'R' AS b, 4 AS c FROM dual
  3    UNION ALL
  4    SELECT 26 AS a, 'T' AS b, 5 AS c FROM dual
  5    UNION ALL
  6    SELECT 26 AS a, 'S' AS b, 2 AS c FROM dual
  7    UNION ALL
  8    SELECT 25 AS a, 'Y' AS b, 2 AS c FROM dual
  9    UNION ALL
 10    SELECT 25 AS a, 'U' AS b, 3 AS c FROM dual
 11    UNION ALL
 12    SELECT 24 AS a, 'X' AS b, 3 AS c FROM dual
 13    UNION ALL
 14    SELECT 22 AS a, 'Z' AS b, 3 AS c FROM dual
 15    UNION ALL
 16    SELECT 21 AS a, 'P' AS b, 3 AS c FROM dual
 17    ),
 18    t AS
 19    ( SELECT a,b,c,row_number() OVER(PARTITION BY a ORDER BY c DESC) rn FROM DATA
 20    )
 21  SELECT a,b,c FROM t WHERE a = &1 AND rn = 1;
Enter value for 1: 26
old  21: SELECT a,b,c FROM t WHERE a = &1 AND rn = 1
new  21: SELECT a,b,c FROM t WHERE a = 26 AND rn = 1

         A B          C
---------- - ----------
        26 T          5

输入a的值25：

SQL> WITH data AS
  2    (SELECT 26 AS a, 'R' AS b, 4 AS c FROM dual
  3    UNION ALL
  4    SELECT 26 AS a, 'T' AS b, 5 AS c FROM dual
  5    UNION ALL
  6    SELECT 26 AS a, 'S' AS b, 2 AS c FROM dual
  7    UNION ALL
  8    SELECT 25 AS a, 'Y' AS b, 2 AS c FROM dual
  9    UNION ALL
 10    SELECT 25 AS a, 'U' AS b, 3 AS c FROM dual
 11    UNION ALL
 12    SELECT 24 AS a, 'X' AS b, 3 AS c FROM dual
 13    UNION ALL
 14    SELECT 22 AS a, 'Z' AS b, 3 AS c FROM dual
 15    UNION ALL
 16    SELECT 21 AS a, 'P' AS b, 3 AS c FROM dual
 17    ),
 18    t AS
 19    ( SELECT a,b,c,row_number() OVER(PARTITION BY a ORDER BY c DESC) rn FROM DATA
 20    )
 21  SELECT a,b,c FROM t WHERE a = &1 AND rn = 1;
Enter value for 1: 25
old  21: SELECT a,b,c FROM t WHERE a = &1 AND rn = 1
new  21: SELECT a,b,c FROM t WHERE a = 25 AND rn = 1

         A B          C
---------- - ----------
        25 U          3

Answer 2

喜欢这个？ -

WITH test
     AS (SELECT 26 AS a, 'R' AS b, 4 AS c FROM dual
         UNION ALL
         SELECT 26 AS a, 'T' AS b, 5 AS c FROM dual
         UNION ALL
         SELECT 26 AS a, 'S' AS b, 2 AS c FROM dual
         UNION ALL
         SELECT 25 AS a, 'Y' AS b, 2 AS c FROM dual
         UNION ALL
         SELECT 25 AS a, 'U' AS b, 3 AS c FROM dual
         UNION ALL
         SELECT 24 AS a, 'X' AS b, 3 AS c FROM dual
         UNION ALL
         SELECT 22 AS a, 'Z' AS b, 3 AS c FROM dual
         UNION ALL
         SELECT 21 AS a, 'P' AS b, 3 AS c FROM dual)
SELECT a, b, c
  FROM (SELECT a, b, c, max(c) OVER (PARTITION BY a) AS max_c
          FROM test
        WHERE A = 26)
 WHERE c = max_c

Answer 3

试试这个。它可能应该工作:)。

class W
{
protected:
  void Stuff() { /*...*/ };
  void Finalize() { /*...*/ };
public:
  virtual ~W() {}
  virtual void Execute() { /*...*/ };
};
class X : public W
{
protected:
  void Stuff() { 
    // X Stuff
    W::Stuff();
  };
public:
  virtual ~X() {}
  virtual void Execute() { 
    X::Stuff();
    W::Finalize();
  };
};

class Y : public X
{
  void Stuff() {
    // Y Stuff
    X::Stuff();
  };
public:
  virtual ~Y() {}
  virtual void Execute() {
    Y::Stuff();
    W::Finalize();
  };
};

Oracle SQL选择查询

3 个答案: