how to throw error in a single query using asp.net

barcode sales balance sales return

1000         1       9            1

1001         0     10           0

1002         0     10           0

1003        0       10             0

we have to throw error as balance stock in 1000 is 9 ,1001 is 10, 1002 is 10, 1003 is 10 and the return is happen means i have to show the error as 1000 is 10(product is available)

through error handling