如何计算另一个表中的一个表的主键？

Question

如何计算5至6列中的另一个表中使用的一个表的主键？

如果table1具有在table2应用于柱d1，d2，d3，d4主键srno。

我想统计table2中使用srno=1,2,3,4 ...等等的次数。

有谁知道该怎么做？

Answer 1

下面的查询将返回的次数列D1，D2，D3和D4在表2（更新）中使用的每个值：

SELECT table1.srno, SUM(cnt) FROM 
    table1, 
    (SELECT d1 AS srno, COUNT(d1) AS cnt FROM table2 GROUP BY d1 
    UNION ALL 
    SELECT d2 AS srno, COUNT(d2) AS cnt FROM table2 GROUP BY d2 
    UNION ALL 
    SELECT d3 AS srno, COUNT(d3) AS cnt FROM table2 GROUP BY d3 
    UNION ALL 
    SELECT d4 AS srno, COUNT(d4) AS cnt FROM table2 GROUP BY d4) AS cnt_tbl 
WHERE table1.srno = cnt_tbl.srno 
GROUP BY table1.srno 

尝试拨弄here.

如果”只重新计算一个特定主键（例如1），然后尝试

SELECT SUM(cnt) FROM 
    (SELECT COUNT(*) AS cnt FROM table2 WHERE d1 = 1 
    UNION ALL 
    SELECT COUNT(*) AS cnt FROM table2 WHERE d2 = 1 
    UNION ALL 
    SELECT COUNT(*) AS cnt FROM table2 WHERE d3 = 1 
    UNION ALL 
    SELECT COUNT(*) AS cnt FROM table2 WHERE d4 = 1) AS cnt_tbl 

小提琴here。

或者没有UNION一个更优雅的解决方案：

SELECT SUM(cnt) FROM 
    (SELECT ((d1=1) + (d2=1) + (d3=1) + (d4=1)) AS cnt 
    FROM table2 
    WHERE d1 = 1 OR d2= 1 OR d3 = 1 OR d4 = 1) AS cnt_tbl 

（Fiddle）

Answer 2

尝试：

SELECT COUNT(PK_COL1_NAME_IN_TABLE2) FROM TABLE2 

见Documentation。