Question

我有以下UNION'声明：

SELECT  8
UNION ALL
SELECT  7
UNION ALL
SELECT  10

...和正常的SELECT声明：

SELECT column1
  FROM table1

现在我的问题是，如何合并两者并得到以下结果

SELECT column1, 10    -- 10 is the biggest element in the UNION statement
  FROM table1

Answer 1

为了回归笛卡尔产品，没有什么特别漂亮：

SELECT t1.column1,
       (SELECT MAX(x.col)
          FROM (SELECT 8 AS col
                UNION ALL
                SELECT 7 AS col
                UNION ALL
                SELECT 10 AS col) x)
 FROM TABLE1 t1

ANSI-89方法：

SELECT t1.column1,
       y.max_col
  FROM TABLE1 t1,
       (SELECT MAX(x.col) AS max_col
          FROM (SELECT 8 AS col
                UNION ALL
                SELECT 7 AS col
                UNION ALL
                SELECT 10 AS col) x) y

ANSI-92方法，使用CROSS JOIN（并非所有数据库都支持）：

    SELECT t1.column1,
           y.max_col
      FROM TABLE1 t1
CROSS JOIN (SELECT MAX(x.col) AS max_col
              FROM (SELECT 8 AS col
                    UNION ALL
                    SELECT 7 AS col
                    UNION ALL
                    SELECT 10 AS col) x) y

Answer 2

怎么样？

SELECT column1, (SELECT MAX(v) FROM (SELECT  8 AS v
                                     UNION ALL
                                     SELECT  7 AS v
                                     UNION ALL
                                     SELECT  10 AS v
                                     ) x)
FROM   table1

Answer 3

SELECT column1, (SELECT MAX(TABLE2.X) 
        FROM (SELECT  8 AS X UNION ALL SELECT  7 AS X UNION ALL SELECT  10 AS X) TABLE2 ) 
     AS MY_MAX
FROM TABLE1

SQL Select语句问题

3 个答案: