SQL select a row X times and insert into new - sql

Question

I am trying to migrate a bunch of data from an old database to a new one, the old one used to just have the number of alarms that occurred on a single row. The new database inserts a new record for each alarm that occurs. Here is a basic version of how it might look. I want to select each row from Table 1 and insert the number of alarm values as new rows into Table 2.
Table 1:
| Alarm ID | Alarm Value |
|--------------|----------------|
| 1 | 3 |
| 2 | 2 |
Should go into the alarm table as the below values.
Table 2:
| Alarm New ID | Value |
|--------------|----------|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 2 |
I want to create a select insert script that will do this, so the select statement will bring back the number of rows that appear in the "Value" column.

Answer 1

A recursive CTE can be convenient for this:
with cte as (
select id, alarm, 1 as n
from t
union all
select id, alarm, n + 1
from cte
where n < alarm
)
select row_number() over (order by id) as alarm_id, id as value
from cte
order by 1
option (maxrecursion 0);
Note: If your values do not exceed 100, then you can remove OPTION (MAXRECURSION 0).

Answer 2

Replicate values out with a CTE.
DECLARE #T TABLE(AlarmID INT, Value INT)
INSERT #T VALUES
(1,3),
(2,2)
;WITH ReplicateAmount AS
(
SELECT AlarmID, Value FROM #T
UNION ALL
SELECT R.AlarmID, Value=(R.Value - 1)
FROM ReplicateAmount R
INNER JOIN #T T ON R.AlarmID = T.AlarmID
WHERE R.Value > 1
)
SELECT
AlarmID = ROW_NUMBER() OVER( ORDER BY AlarmID),
Value = AlarmID --??
FROM
ReplicateAmount
ORDER BY
AlarmID
This answers your question. I would think the query below would be more useful, however, you did not include usage context.
SELECT
AlarmID,
Value
FROM
ReplicateAmount
ORDER BY
AlarmID

Answer 3

Rather than using an rCTE, which is recursive (as the name suggests) and will fail at 100 rows, you can use a Tally table, which tend to be far faster as well:
WITH N AS(
SELECT N
FROM (VALUES(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL))N(N)),
Tally AS(
SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS I
FROM N N1, N N2, N N3)
SELECT ROW_NUMBER() OVER (ORDER BY V.AlarmID,T.I) AS AlarmNewID,
V.AlarmID
FROM (VALUES(1,3),(2,2))V(AlarmID,AlarmValue)
JOIN Tally T ON V.AlarmValue >= T.I;