Send to all instead of one
<p>I am new to SQL Server and I am trying to run the following query, but I get the following error </p>

<blockquote>
  <p>Msg 512, Level 16, State 1, Line 20<br>
  Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, &lt;, &lt;= , >, >= or when the subquery is used as an expression.</p>
  
  <p>Msg 515, Level 16, State 2, Line 35<br>
  Cannot insert the value NULL into column 'UserUID', table 'PS_Billing.dbo.Users_Product'; column does not allow nulls. INSERT fails.</p>
</blockquote>

<p>Here is my query:</p>

<pre><code>DECLARE @UserID varchar(18), @UserUID bigint, @ItemID int,
        @ItemCount tinyint, @OrderNumber int, @BuyDate datetime, 
        @ProductCode varchar(20), @Slot tinyint, @empty smallint

-- Send Item to User Bank 
-- ----------- CONFIG  ------------------
-- UserID:
SET @UserID = 'Reset'

-- ItemID:
SET @ItemID = 100047

-- Item Count:
SET @ItemCount = 8

-- Produkt Description (max. 20 char.)
SET @ProductCode = ' '

-- --------------------------------------
SET @OrderNumber = 1
SET @BuyDate = GETDATE()

SET @UserUID = (SELECT UserUID 
                FROM PS_UserData.dbo.Users_Master 
                WHERE UserID &lt;&gt; @UserID)

SET @Slot = 0
SET @empty = -1

WHILE (@Slot &lt;= 239)
BEGIN 
    SET @empty = (SELECT COUNT(Slot) 
                  FROM PS_Billing.dbo.Users_Product 
                  WHERE UserUID = @UserUID AND Slot = @Slot)

    IF (@empty &lt;= 0) 
        BREAK
    ELSE  
        SET @Slot = @Slot+1
    END

    INSERT INTO PS_Billing.dbo.Users_Product (UserUID, Slot, ItemID, ItemCount, ProductCode, OrderNumber, BuyDate)
    VALUES (@UserUID, @Slot, @ItemID, @ItemCount, @ProductCode, @OrderNumber, @BuyDate)

    PRINT ''

    IF @Slot &lt; 239 
       PRINT 'Used slot: '+CONVERT(varchar(3), @Slot)

    IF @Slot = 239 
       PRINT 'THERE IS NO FREE SLOT ANYMORE (240/240 SLOTS USED)!'
</code></pre>

<p>So, what I am trying to make is a query that sends the listed item to all players in my database, not just to one. </p>