The data quality team wants to measure how much the BI and Finance customer lists agree.
Using bi_customers and fin_customers, prepare one summary row with three counts:
01only_bi: Distinct customers found in BI but not Finance.
02only_fin: Distinct customers found in Finance but not BI.
03in_both: Distinct customers recorded in both systems.
Each customer should contribute to exactly one of these categories.
Ordering: Return a single row; no sorting is required.