How to use a While Loop when returning multiple Values using a variable? - tsql

Question

I'm trying to return multiple values for my Log Backups, cause when I use a Set variable it only returns one value. I thought about using a while loop as this will loop and return all my logs close to the restore point. However returns back NULL Value. When I use a Set Variable I'm getting the latest Transaction Log file back but I'm not getting the previous logs before that after the latest Full I think this is to do with me using a Set variable as this only outputs one value.
DECLARE #LogbackupFile nvarchar(max),
#DatabaseName varchar(500) = 'ns_lots_of_vlfs',
#DiffDate datetime = null,
#LogDate datetime = null,
#RestoreDate datetime = '2023-01-30 12:00:06.000',
#FullBackupFile nvarchar(max),
#FullBackupDate datetime
SELECT
TOP 1 #FullBackupFile = bmf.physical_device_name,
#FullBackupDate = bs.backup_finish_date
FROM
msdb.dbo.backupmediafamily bmf
INNER JOIN msdb.dbo.backupset bs ON bs.media_set_id = bmf.media_set_id
WHERE
bs.type = 'D'
AND bs.database_name = #DatabaseName
AND bs.backup_finish_date <= #RestoreDate
ORDER BY
backup_finish_date DESC IF OBJECT_ID('tempdb..#TempTable_log') IS NOT NULL
DROP
TABLE #TempTable_log
SELECT
bmf.family_sequence_number,
bmf.media_family_id,
bmf.media_count,
bmf.logical_device_name,
bmf.physical_device_name,
bmf.device_type,
bmf.physical_block_size,
bmf.mirror,
bs.backup_set_id,
bs.backup_set_uuid,
bs.first_family_number,
bs.first_media_number,
bs.last_family_number,
bs.last_media_number,
bs.catalog_family_number,
bs.catalog_media_number,
bs.position,
bs.expiration_date,
bs.software_vendor_id,
bs.name,
bs.description,
bs.user_name,
bs.software_major_version,
bs.software_minor_version,
bs.software_build_version,
bs.time_zone,
bs.mtf_minor_version,
bs.first_lsn,
bs.last_lsn,
bs.checkpoint_lsn,
bs.database_backup_lsn,
bs.database_creation_date,
bs.backup_start_date,
bs.backup_finish_date,
bs.type,
bs.sort_order,
bs.code_page,
bs.compatibility_level,
bs.database_version,
bs.backup_size,
bs.database_name,
bs.server_name,
bs.machine_name,
bs.flags,
bs.unicode_locale,
bs.unicode_compare_style,
bs.collation_name,
bs.is_password_protected,
bs.recovery_model,
bs.has_bulk_logged_data,
bs.is_snapshot,
bs.is_readonly,
bs.is_single_user,
bs.has_backup_checksums,
bs.is_damaged,
bs.begins_log_chain,
bs.has_incomplete_metadata,
bs.is_force_offline,
bs.is_copy_only,
bs.first_recovery_fork_guid,
bs.last_recovery_fork_guid,
bs.fork_point_lsn,
bs.database_guid,
bs.family_guid,
bs.differential_base_lsn,
bs.differential_base_guid,
bs.compressed_backup_size,
bs.key_algorithm,
bs.encryptor_thumbprint,
bs.encryptor_type INTO #TempTable_log
FROM
msdb.dbo.backupmediafamily bmf
INNER JOIN msdb.dbo.backupset bs ON bs.media_set_id = bmf.media_set_id
WHERE
bs.database_name = #DatabaseName
AND bs.backup_finish_date <= #RestoreDate
AND bs.backup_finish_date > ISNULL(#DiffDate, #FullBackupDate)
AND bs.type = 'L'
AND bmf.physical_device_name LIKE '%Log%'
WHILE (#LogbackupFile IS NOT NULL)
BEGIN
SELECT
#LogBackupFile = bmf.physical_device_name
FROM
#TempTable_log bmf
WHERE
bmf.database_name = #DatabaseName
AND bmf.backup_finish_date <= #RestoreDate
AND bmf.backup_finish_date > ISNULL(#DiffDate, #FullBackupDate)
AND bmf.type = 'L'
AND bmf.physical_device_name LIKE '%Log%' PRINT #LogBackupFile END
SELECT
#LogbackupFile

Answer 1

It's not fully clear to me what you're asking, but it sounds like the problem is you want to do this at the end:
SELECT #LogbackupFile
Where #LogbackupFile was populated in a query like this:
SELECT
#LogBackupFile = bmf.physical_device_name
FROM
#TempTable_log bmf
WHERE
bmf.database_name = #DatabaseName
AND bmf.backup_finish_date <= #RestoreDate
AND bmf.backup_finish_date > ISNULL(#DiffDate, #FullBackupDate)
AND bmf.type = 'L'
AND bmf.physical_device_name LIKE '%Log%'
When what you should do is just select the column and not worry about trying to set a variable at all:
SELECT
bmf.physical_device_name As LogBackupFile
FROM
#TempTable_log bmf
WHERE
bmf.database_name = #DatabaseName
AND bmf.backup_finish_date <= #RestoreDate
AND bmf.backup_finish_date > ISNULL(#DiffDate, #FullBackupDate)
AND bmf.type = 'L'
AND bmf.physical_device_name LIKE '%Log%'
Now your client code can look at the entire result set.
Even better, looking through the code I'm extremely confident this entire thing could be re-written as a single SQL query, with no temp tables or variables at all other than the #DatabaseName, #RestoreDate, and #Diffdate inputs. However, there a few places where the desire to express the code in a procedural paradigm, rather than set-based, is clouding the intent. Also, it is probably easier to grab the #FullBackupDate value in a separate query.
DECLARE #DatabaseName varchar(500) = 'ns_lots_of_vlfs',
#DiffDate datetime = null,
#RestoreDate datetime = '2023-01-30 12:00:06.000',
#FullBackupDate datetime
SELECT TOP 1 #FullBackupDate = bs.backup_finish_date
FROM msdb.dbo.backupmediafamily bmf
INNER JOIN msdb.dbo.backupset bs ON bs.media_set_id = bmf.media_set_id
WHERE bs.type = 'D'
AND bs.database_name = #DatabaseName
AND bs.backup_finish_date <= #RestoreDate
ORDER BY bs.backup_finish_date DESC
SELECT bmf.physical_device_name As LogBackupFile
FROM msdb.dbo.backupmediafamily bmf
INNER JOIN msdb.dbo.backupset bs ON bs.media_set_id = bmf.media_set_id
WHERE bs.database_name = #DatabaseName
AND bs.backup_finish_date <= #RestoreDate
AND bs.backup_finish_date > ISNULL(#DiffDate, #FullBackupDate)
AND bs.type = 'L'
AND bmf.physical_device_name LIKE '%Log%'
And again: this should send the appropriate data back to the client. If you're having trouble retrieving this data perhaps try posting your client code.