如何給mysql數據庫中限制人數賦予不同的值？

Question

我有學生和班級。 每個學生有一個exam_place_id和教室 每個教室都有自己的坐位限制。 所以我必須根據學生的數量給予每個學生教室。

例如在伊斯坦布爾（exam_place_id = 11）我現在有530名學生。

和類配額就像

Class 1 - number of students can sit : 19 
Class 2 - number of students can sit : 26 
Class 3 - number of students can sit : 29 
Class 4 - number of students can sit : 24 
Class 5 - number of students can sit : 31 
Class 6 - number of students can sit : 22 
Class 7 - number of students can sit : 24 
Class 8 - number of students can sit : 29 
Class 9 - number of students can sit : 24 
Class 10 - number of students can sit : 25 
Class 11 - number of students can sit : 28 
Class 12 - number of students can sit : 24 
Class 13 - number of students can sit : 22 
Class 14 - number of students can sit : 28 
Class 15 - number of students can sit : 28 
Class 16 - number of students can sit : 27 
Class 17 - number of students can sit : 64 
Class 18 - number of students can sit : 64 

所以依班配額我會更新學生的班級

update students set class = "Class 1" where payStatus = 1 and is_completed = 1 and exam_place_id =11 and class = 0 limit 19 

update users set class = "Class 2" where payStatus = 1 and is_completed = 1 and exam_place_id =11 and class = 0 limit 26 

所以我會不會從表19級的用戶，並檢查他們的其中的類值爲零（未定義）我將用我的班級號碼更新它們。但沒有工作它覆蓋之前，即使我嘗試更新學生與 class = 0

什麼是我可以嘗試的任何其他解決方案？

Answer 1

據我們所知class列類型爲varchar，所以0是不可能的值。您是否想要檢查列值是否爲NULL或爲空？

UPDATE students SET class = "Class 1" 
WHERE payStatus = 1 AND is_completed = 1 AND 
     exam_place_id =11 AND (class IS NULL OR class = '') 
LIMIT 19 

Answer 2

也許這樣的事情？

UPDATE TOP (19) users set class = "Class 2" where payStatus = 1 and is_completed = 1 and exam_place_id =11 and class = 0