如何计算另一个表中一个表的主键？

Question

如何计算在5到6列的另一个表中使用的一个表的主键？

如果table1包含srno列table2，d1，d2，d3中使用的主键d4 }。

我想计算srno=1,2,3,4中使用table2 ...等的次数。

有谁知道怎么做???

Answer 1

以下查询将返回表2中列d1，d2，d3和d4中使用的每个值的次数（已更新）：

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

尝试小提琴here.

如果您只计算一个特定主键（例如1），请尝试

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的更优雅的解决方案：

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

请参阅Documentation。