Sending first half records of the table to target

1. Drag source and target into the mapping.
2. Let us assume EMP is source, and create a new table say T_EMP with same structure as EMP.
3. Create the mapping as shown below:

4. Now edit Source Qualifier tranformation and click on properties tab.
5. Enter the following query in SQL Query property:

SELECT * FROM emp WHERE ROWNUM <= (SELECT COUNT(*)/2 FROM emp

6. Save the mapping.
7. Finally create session, Workflow and run thee workflow.