TECHNO SUBBU :
私のテーブル
mysql> desc attendance;
+--------+------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+------------+------+-----+---------+----------------+
| aid | bigint(20) | NO | PRI | NULL | auto_increment |
| sid | int(10) | YES | MUL | NULL | |
| cid | bigint(20) | YES | MUL | NULL | |
| ttid | bigint(20) | YES | MUL | NULL | |
| did | int(3) | YES | MUL | NULL | |
| date | date | YES | | NULL | |
| hour | varchar(3) | YES | | NULL | |
| stuid | bigint(20) | YES | MUL | NULL | |
| status | varchar(8) | YES | | NULL | |
+--------+------------+------+-----+---------+----------------+
9 rows in set (0.47 sec)
そして、それの値は、
mysql> select * from attendance;
+-----+------+------+------+------+------------+------+-------+---------+
| aid | sid | cid | ttid | did | date | hour | stuid | status |
+-----+------+------+------+------+------------+------+-------+---------+
| 1 | 2 | 13 | 4 | 3 | 2020-03-25 | p1 | 16 | present |
| 2 | 2 | 13 | 4 | 3 | 2020-03-25 | p1 | 17 | absent |
| 3 | 2 | 13 | 4 | 3 | 2020-03-25 | p1 | 18 | present |
| 4 | 2 | 13 | 4 | 3 | 2020-03-25 | p1 | 19 | absent |
| 5 | 2 | 13 | 4 | 3 | 2020-03-25 | p1 | 20 | present |
| 6 | 2 | 13 | 4 | 3 | 2020-03-25 | p1 | 15 | absent |
| 7 | 2 | 13 | 2 | 2 | 2020-03-17 | p6 | 16 | present |
| 8 | 2 | 13 | 2 | 2 | 2020-03-17 | p6 | 17 | absent |
| 9 | 2 | 13 | 2 | 2 | 2020-03-17 | p6 | 18 | present |
| 10 | 2 | 13 | 2 | 2 | 2020-03-17 | p6 | 19 | absent |
| 11 | 2 | 13 | 2 | 2 | 2020-03-17 | p6 | 20 | present |
| 12 | 2 | 13 | 2 | 2 | 2020-03-17 | p6 | 15 | absent |
| 13 | 2 | 13 | 4 | 3 | 2020-03-25 | p2 | 16 | present |
| 14 | 2 | 13 | 4 | 3 | 2020-03-25 | p2 | 17 | present |
| 15 | 2 | 13 | 4 | 3 | 2020-03-25 | p2 | 18 | present |
| 16 | 2 | 13 | 4 | 3 | 2020-03-25 | p2 | 19 | present |
| 17 | 2 | 13 | 4 | 3 | 2020-03-25 | p2 | 20 | present |
| 18 | 2 | 13 | 4 | 3 | 2020-03-25 | p2 | 15 | present |
| 19 | 2 | 13 | 4 | 3 | 2020-03-25 | p8 | 16 | absent |
| 20 | 2 | 13 | 4 | 3 | 2020-03-25 | p8 | 17 | absent |
| 21 | 2 | 13 | 4 | 3 | 2020-03-25 | p8 | 18 | present |
| 22 | 2 | 13 | 4 | 3 | 2020-03-25 | p8 | 19 | present |
| 23 | 2 | 13 | 4 | 3 | 2020-03-25 | p8 | 20 | present |
| 24 | 2 | 13 | 4 | 3 | 2020-03-25 | p8 | 15 | absent |
+-----+------+------+------+------+------------+------+-------+---------+
24 rows in set (0.00 sec)
今、私はそれが起こっているなぜそれが0にそれぞれ、すべての列の値のリターンを返すテーブルグループ間0でテーブルが、戻り値をグループ化するつもりです。私の代わりの0缶誰もが、この論理エラーを解決あるかない必要がありますか?
GMB:
sum(case when hour = 'P1' then status else 'null' end) p1
問題は、あなたが数字とsumingされていることであるlitteral文字列を 'null'
。
あなたは望んでいたnull
、まだ良いか- (引用符なし)0
sum(case when hour = 'p1' then status else 0 end) p1
以下のような式を短縮することができますMySQLでは数値コンテキストでは1/0として真/偽条件を評価することを注意:
sum(hour = 'p1') p1