通过合并明细字段将主数据表和明细表合并为一行

Question

I have 2 tables, one which is the master the other the details. They have a 1 to many relationship:

MasterTable
------------
id (pk)
col1


DetailTable
------------
id (pk)
mid (fk to MasterTable id)
col1

An example of how data would look would be as such:

MasterTable

ID   
---
1     
2
3
4
5 


DetailTable

ID | MID   | COL1  |
---|-------|-------|
1     1       BIRD     
2     1       DOG                      
3     1       DOG --Duplicates are allowed for the same MID
4     1       CAT
5     2       CAT
6     5       FISH

For the detail table the possible values for col1 are:

• BIRD
• DOG
• CAT
• FISH
• MOUSE

I then need to create a query which will layout for each id in the master table to see if they have any of these values. So the final query result would look like this:

MasterID | BIRD | DOG | CAT | FISH | MOUSE
-----------------------------------------------------
1           Y     Y      Y
2                        Y
3
4                        
5                              Y

So I am collapsing the detail table into one row in the final result. I am unsure how to create this query though.

I was trying something like this, but it doesn't work:

SELECT MASTERTABLE.ID, 
CASE WHEN DETAILTABLE.col1 = 'BIRD' THEN 'Y' ELSE NULL END AS BIRD,
CASE WHEN DETAILTABLE.col1 = 'DOG' THEN 'Y' ELSE NULL END AS DOG, 
CASE WHEN DETAILTABLE.col1 = 'CAT' THEN 'Y' ELSE NULL END AS CAT, 
CASE WHEN DETAILTABLE.col1 = 'FISH' THEN 'Y' ELSE NULL END AS FISH, 
CASE WHEN DETAILTABLE.col1 = 'MOUSE' THEN 'Y' ELSE NULL END AS MOUSE
FROM MASTERTABLE LEFT JOIN DETAILTABLE ON MASTERTABLE.ID = DETAILTABLE.mid;

Answer 1

Pivoting, whether it is done with the PIVOT operator (starting from Oracle version 11.1) or with conditional aggregation (version 10.2 or earlier), works equally well on any set of rows, whether that is a single table, the result of joining two tables, or the result of any other set operation permitted in SQL (another aggregation, a UNION ALL , or anything else).

You were pretty close in your attempt. All you have to do is to GROUP BY MASTERTABLE.ID (since you want only one row per MASTERTABLE.ID ) and to take the MAX of all those CASE expressions: if at least one of them is 'Y' then the MAX is 'Y' , otherwise it is NULL .

So:

In your query, EXACTLY AS IT IS,

• change CASE .... END as BIRD to MAX(CASE ... END) as BIRD
• add GROUP BY MASTERTABLE.ID at the end