what are the details of the cmi masters that have the cross reference code 'Tax'?
SELECT T1.cmi_details FROM Customer_Master_Index AS T1 JOIN CMI_Cross_References AS T2 ON T1.master_customer_id  =  T2.master_customer_id WHERE T2.source_system_code  =  'Tax'
details of the cmi masters refers to T1.cmi_details; have the cross reference code 'Tax' refers to WHERE T2.source_system_code = 'Tax'; joining tables refers to JOIN;