CREATE TABLE CMI_Cross_References (master_customer_id VARCHAR2, source_system_code VARCHAR2)
CREATE TABLE Customer_Master_Index (cmi_details VARCHAR2, master_customer_id VARCHAR2)

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'
SELECT "T1"."cmi_details" FROM "Customer_Master_Index" "T1" JOIN "CMI_Cross_References" "T2" ON "T1"."master_customer_id" = "T2"."master_customer_id" AND "T2"."source_system_code" = 'Tax'