Check for duplicate record in SQL database before doing INSERT

Question

Hey guys,
       This is part powershell app doing a SQL insert. BUt my question really relates to the SQL insert. I need to do a check of the database PRIOR to doing the insert to check for duplicate records and if it exists then that record needs
to be overwritten. I'm not sure how to accomplish this task. My back end is a SQL 2000 Server. I'm piping the data into my insert statement from a powershell FileSystemWatcher app. In my scenario here if the file dumped into a directory starts with I it gets
written to a SQL database otherwise it gets written to an Access Table. I know silly, but thats the environment im in. haha.
Any help is appreciated.
Thanks in Advance
Rich T.
#### DEFINE WATCH FOLDERS AND DEFAULT FILE EXTENSION TO WATCH FOR ####
            $cofa_folder = '\\cpsfs001\Data_pvs\TestCofA'
            $bulk_folder = '\\cpsfs001\PVS\Subsidiary\Nolwood\McWood\POD'
            $filter = '*.tif'
            $cofa = New-Object IO.FileSystemWatcher $cofa_folder, $filter -Property @{ IncludeSubdirectories = $false; EnableRaisingEvents= $true; NotifyFilter = [IO.NotifyFilters]'FileName, LastWrite' }
            $bulk = New-Object IO.FileSystemWatcher $bulk_folder, $filter -Property @{ IncludeSubdirectories = $false; EnableRaisingEvents= $true; NotifyFilter = [IO.NotifyFilters]'FileName, LastWrite' }
#### CERTIFICATE OF ANALYSIS AND PACKAGE SHIPPER PROCESSING ####
            Register-ObjectEvent $cofa Created -SourceIdentifier COFA/PACKAGE -Action {
       $name = $Event.SourceEventArgs.Name
       $changeType = $Event.SourceEventArgs.ChangeType
       $timeStamp = $Event.TimeGenerated
#### CERTIFICATE OF ANALYSIS PROCESS BEGINS ####
            $test=$name.StartsWith("I")
     if ($test -eq $true) {
            $pos = $name.IndexOf(".")
       $left=$name.substring(0,$pos)
       $pos = $left.IndexOf("L")
       $tempItem=$left.substring(0,$pos)
       $lot = $left.Substring($pos + 1)
       $item=$tempItem.Substring(1)
            Write-Host "in_item_key $item in_lot_key $lot imgfilename $name in_cofa_crtdt $timestamp"  -fore green
            Out-File -FilePath c:\OutputLogs\CofA.csv -Append -InputObject "in_item_key $item in_lot_key $lot imgfilename $name in_cofa_crtdt $timestamp"
            start-sleep -s 5
            $conn = New-Object System.Data.SqlClient.SqlConnection("Data Source=PVSNTDB33; Initial Catalog=adagecopy_daily; Integrated Security=TRUE")
            $conn.Open()
            $insert_stmt = "INSERT INTO in_cofa_pvs (in_item_key, in_lot_key, imgfileName, in_cofa_crtdt) VALUES ('$item','$lot','$name','$timestamp')"
            $cmd = $conn.CreateCommand()
            $cmd.CommandText = $insert_stmt
            $cmd.ExecuteNonQuery()
            $conn.Close()
#### PACKAGE SHIPPER PROCESS BEGINS ####
          elseif ($test -eq $false) {
            $pos = $name.IndexOf(".")
       $left=$name.substring(0,$pos)
       $pos = $left.IndexOf("O")
       $tempItem=$left.substring(0,$pos)
       $order = $left.Substring($pos + 1)
       $shipid=$tempItem.Substring(1)
            Write-Host "so_hdr_key $order so_ship_key $shipid imgfilename $name in_cofa_crtdt $timestamp"  -fore green
            Out-File -FilePath c:\OutputLogs\PackageShipper.csv -Append -InputObject "so_hdr_key $order so_ship_key $shipid imgfilename $name in_cofa_crtdt $timestamp"
Rich Thompson

Answer 1

Hi
Since SQL Server 2000 has been out of support, I recommend you to upgrade the SQL Server 2000 to a higher version, such as SQL Server 2005 or SQL Server 2008.
According to your description, you can try the following methods to check duplicate record in SQL Server.
1. You can use
RAISERROR to check the duplicate record, if exists then RAISERROR unless insert accordingly, code block is given below:
IF EXISTS (SELECT 1 FROM TableName AS t
WHERE t.Column1 = @ Column1
AND t.Column2 = @ Column2)
BEGIN
RAISERROR(‘Duplicate records’,18,1)
END
ELSE
BEGIN
INSERT INTO TableName (Column1, Column2, Column3)
SELECT @ Column1, @ Column2, @ Column3
END
2. Also you can create UNIQUE INDEX or UNIQUE CONSTRAINT on the column of a table, when you try to INSERT a value that conflicts with the INDEX/CONSTRAINT, an exception will be thrown. 
Add the unique index:
CREATE UNIQUE INDEX Unique_Index_name ON TableName(ColumnName)
Add the unique constraint:
ALTER TABLE TableName
ADD CONSTRAINT Unique_Contraint_Name
UNIQUE (ColumnName)
Thanks
Lydia Zhang