Question

尝试获得稍微复杂的sql语句，但似乎无法使语法正确。尝试在两个不同的表中选择各种列的计数。

SELECT 
     SUM(ColumninTable1), 
     SUM(Column2inTable1), 
     COUNT(DISTINCT(Column3inTable1)) 
FROM TABLE1

这是有效的，但我不能为我的生活弄清楚如何使用什么语法添加COUNT（DISTINCT（Column1inTable2）FROM TABLE2。

Answer 1

您可以采取以下几种解决方案：

取消FULL OUTER JOIN

SELECT 
    SUM(MYTABLE.ID) as theSum,
    COUNT(DISTINCT MYTABLE.SOMEVALUE) as theCount,
    COUNT(DISTINCT MYOTHERTABLE.SOMEOTHERVALUE) as theOtherCount
FROM MYTABLE
FULL OUTER JOIN MYOTHERTABLE ON 1=0

UNION两个查询并将其他表的列保留为空

SELECT 
    MAX(theSum) as theSum, 
    MAX(theCount) as theCount, 
    MAX(theOtherCount) AS theOtherCount
FROM (
    SELECT
        SUM(ID) as theSum,
        COUNT(DISTINCT SOMEVALUE) as theCount,
        NULL as theOtherCount
    FROM MYTABLE
    UNION ALL
    SELECT
        NULL,
        NULL,
        COUNT(DISTINCT SOMEOTHERVALUE)
    FROM MYOTHERTABLE
)

针对单个记录表查询'每列查询'（例如RDB$DATABASE）

SELECT
    (SELECT SUM(ID) FROM MYTABLE) as theSum,
    (SELECT COUNT(DISTINCT SOMEVALUE) FROM MYTABLE) as theCount,
    (SELECT COUNT(DISTINCT SOMEOTHERVALUE) FROM MYOTHERTABLE) as theOtherCount
FROM RDB$DATABASE

每张桌子的CTE +交叉加入

WITH query1 AS (
    SELECT
        SUM(ID) as theSum,
        COUNT(DISTINCT SOMEVALUE) as theCount
    FROM MYTABLE
),
query2 AS (
    SELECT
        COUNT(DISTINCT SOMEOTHERVALUE) as theOtherCount
    FROM MYOTHERTABLE
)
SELECT 
    query1.theSum,
    query1.theCount,
    query2.theOtherCount
FROM query1
CROSS JOIN query2

可能还有一些解决方案。您可能想问自己是否值得努力想出一个（复杂的，难以理解的）单个查询来获取这些数据，这两个查询足够，更容易理解，并且在大型数据集的情况下：两个单独的查询可能会更快。

Answer 2

在这种情况下，所有“count”将返回相同的值。

尝试使用子查询执行相同的操作：

  Select 
   (Select count (*) from Table1), 
   (Select count (*) from table2) 
  from Table3

ODBC Firebird Sql查询 - 语法

2 个答案: