I have 2 tables, one with the ID and its count and the other with the names belonging to the respective IDs. They need to be joined so that the end result is a table with count of 1 in each row and the respective names next to them. Note that the number of names in table 2 is less than the count in table 1 for the same ID in some cases.
Table 1
ID | Count
-----------
100 | 3
101 | 2
102 | 4
Table 2
ID | Name
----------
100 | abc
100 | def
101 | ghi
101 | jkl
102 | mno
102 | pqr
102 | stu
Result
ID | Count | Name
------------------
100 | 1 | abc
100 | 1 | def
100 | 1 |
101 | 1 | ghi
101 | 1 | jkl
102 | 1 | mno
102 | 1 | pqr
102 | 1 | stu
102 | 1 |
I'm using TSQL for this and my current query converts table 1 into multiple rows in the result table; then it inserts individual names from table 2 into the result table through a loop. I'm hoping there must be a simpler or more efficient way to do this as the current method takes considerable amount of time. If there is, please let me know.
The first thing that comes to mind for me involves using a Number table, which you could create (as a one-time task) like this:
CREATE TABLE numbers (
ID INT
)
DECLARE @CurrentNumber INT, @MaxNumber INT
SET @MaxNumber = 100 -- Choose a value here which you feel will always be greater than MAX(table1.Count)
SET @CurrentNumber = 1
WHILE @CurrentNumber <= @MaxNumber
BEGIN
INSERT INTO numbers VALUES (@CurrentNumber)
SET @CurrentNumber = @CurrentNumber + 1
END
Once you have a numbers table, you can solve this problem like this:
SELECT one.ID,
1 AS [Count],
ISNULL(two.Name,'') AS Name
FROM table1 one
JOIN numbers n ON n.ID <= CASE WHEN one.[Count] >= (SELECT COUNT(1) FROM table2 two WHERE one.ID = two.ID)
THEN one.[Count]
ELSE (SELECT COUNT(1) FROM table2 two WHERE one.ID = two.ID)
END
LEFT JOIN (SELECT ID,
Name,
ROW_NUMBER() OVER (PARTITION BY ID ORDER BY ID) AS RecordNo
FROM table2) two ON one.ID = two.ID
AND two.RecordNo = n.ID