SQL 比较多个行或分区以找到匹配项

Question

我正在处理的数据库是 DB2，我遇到了类似于以下情况的问题：

Table Structure
-------------------------------
| Teacher Seating Arrangement |
-------------------------------
| PK | seat_argmt_id          |
|    | teacher_id             |
-------------------------------

-----------------------------
| Seating Arrangement       |
-----------------------------
|PK FK | seat_argmt_id      |
|PK    | Row_num            |
|PK    | seat_num           |
|PK    | child_name         |
-----------------------------

Table Data
------------------------------
| Teacher Seating Arrangement|
------------------------------
| seat_argmt_id | teacher_id |
|         1     |     1      |
|         2     |     1      |
|         3     |     1      |
|         4     |     1      |
|         5     |     2      |
------------------------------

---------------------------------------------------
| Seating Arrangement                             |
---------------------------------------------------
| seat_argmt_id | row_num | seat_num | child_name |
|        1      |    1    |    1     |     Abe    |
|        1      |    1    |    2     |     Bob    |
|        1      |    1    |    3     |     Cat    |
|               |         |          |            |
|        2      |    1    |    1     |     Abe    |
|        2      |    1    |    2     |     Bob    |
|        2      |    1    |    3     |     Cat    |
|               |         |          |            |
|        3      |    1    |    1     |     Abe    |
|        3      |    1    |    2     |     Cat    |
|        3      |    1    |    3     |     Bob    |
|               |         |          |            |
|        4      |    1    |    1     |     Abe    |
|        4      |    1    |    2     |     Bob    |
|        4      |    1    |    3     |     Cat    |
|        4      |    2    |    2     |     Dan    |
---------------------------------------------------

我想看看哪里有重复的老师座位安排。重复是指 row_num、seat_num 和 child_name 在不同的 seat_argmt_id 中相同的地方 teacher_id。因此，根据上面提供的数据，只有座位 ID 1 和 2 是我想要撤回的，因为它们在除 seat id 之外的所有内容上都是重复的。如果第 2 个 table 上的所有 children 都是准确的（没有主键和外键，在这种情况下是 seat_argmt_id），我想看看。

我最初的想法是做一个 count(*) group by row#, seat#, and child。所有计数 > 1 的东西都意味着它是一个骗局，而 = 1 意味着它是独一无二的。不过，该逻辑仅在您比较单行时才有效。我需要比较多行。我无法通过 SQL 找出一种方法来做到这一点。我的解决方案涉及到 SQL 之外并且有效（可能）。我只是想知道在 DB2 中是否有办法做到这一点。

Answer 1

这是你想要的吗？

select d.teacher_id, sa.row_num, sa.seat_num, sa.child_name
from seatingarrangement sa join
     data d
     on sa.seat_argmt_id = d.seat_argmt_id
group by d.teacher_id, sa.row_num, sa.seat_num, sa.child_name
having count(*) > 1;

编辑：

如果你想找到两个相同的排列:

select sa1.seat_argmt_id, sa2.seat_argmt_id
from seatingarrangement sa1 join
     seatingarrangement sa2
     on sa1.seat_argmt_id < sa2.seat_argmt_id and
        sa1.row_num = sa2.row_num and
        sa1.seat_num = sa2.seat_num and
        sa1.child_name = sa2.child_name
group by sa1.seat_argmt_id, sa2.seat_argmt_id
having count(*) = (select count(*) from seatingarrangement sa where sa.seat_argmt_id = sa1.seat_argmt_id) and
       count(*) = (select count(*) from seatingarrangement sa where sa.seat_argmt_id = sa2.seat_argmt_id);

这会找到两个排列之间的匹配项，然后验证计数是否正确。

SQL 比较多个行或分区以找到匹配项

SQL compare multiple rows or partitions to find matches

sql

db2