如何在多個列上使用不同的計數？

Question

輸入：

id sem1 sem2 sem3 sem4 sem5 sem6 sem7 
1 S O  S R null null null 
2 O O  R R S null null 

所需的輸出：

id O R S 
1 1 1 2 
2 2 2 1 

Answer 1

如果你的數據庫支持APPLY/UNPIVOT運營商然後使用這個

CROSS APPLY方法

SELECT id, 
     SUM(CASE WHEN val = 'O' THEN 1 ELSE 0 END) O, 
     SUM(CASE WHEN val = 'R' THEN 1 ELSE 0 END) R, 
     SUM(CASE WHEN val = 'S' THEN 1 ELSE 0 END) S 
FROM mytable 
     CROSS apply (VALUES (sem1), 
          (sem2), 
          (sem3), 
          (sem4), 
          (sem5), 
          (sem6), 
          (sem7)) cs(val) 
GROUP BY id 

• SQL FIDDLE DEMO

UNPIVOT方法

SELECT id, 
     SUM(CASE WHEN val = 'O' THEN 1 ELSE 0 END) O, 
     SUM(CASE WHEN val = 'R' THEN 1 ELSE 0 END) R, 
     SUM(CASE WHEN val = 'S' THEN 1 ELSE 0 END) S 
FROM (SELECT * 
     FROM mytable) a 
     UNPIVOT (val 
       FOR col IN (sem1, 
          sem2, 
          sem3, 
          sem4, 
          sem5, 
          sem6, 
          sem7)) upv 
GROUP BY id 

• SQL FIDDLE DEMO

我個人偏好CROSS APPLY方法在UNPIVOT，因爲它是更具有可讀性。性能明智兩者將是相同的