You can enter an SQL override if you want to customize the SELECT statement in the SQL query. The SQL statement you enter on the Transformations view of the Mapping tab overrides any customized SQL query that you set in the Designer when you configure the Source Qualifier transformation.
The SQL query also overrides any key range and filter condition that you enter for a source partition. So, if you also enter a key range and source filter, the Integration Service uses the SQL query override to extract source data.
If you create a key that contains null values, you can extract the nulls by creating another partition and entering an SQL query or filter to extract null values.
To enter an SQL query for each partition, click the Browse button in the SQL Query field. Enter the query in the SQL Editor dialog box, and then click OK.
If you entered an SQL query in the Designer when you configured the Source Qualifier transformation, that query appears in the SQL Query field for each partition. To override this query, click the Browse button in the SQL Query field, revise the query in the SQL Editor dialog box, and then click OK.