SQL IF EXIST in a script

If you are using SQL Server, look into using merge.

MERGE INTO table_name WITH (HOLDLOCK) USING table_name ON (condition)
WHEN MATCHED THEN UPDATE SET column1 = value1 [, column2 = value2 …]
WHEN NOT MATCHED THEN INSERT (column1 [, column2 …]) VALUES (value1 [, value2 …])