List benefit ID, please.
SELECT T1.source_system_code , T2.council_tax_id FROM CMI_Cross_References AS T1 JOIN Benefits_Overpayments AS T2 ON T1.cmi_cross_ref_id  =  T2.cmi_cross_ref_id
List benefit ID refers to selecting council_tax_id from Benefits_Overpayments; requires joining CMI_Cross_References on cmi_cross_ref_id to access council_tax_id;