CodePudding user response:

 SELECT * FROM (
SELECT 
ROW_NUMBER () OVER (PARTITION BY SFZH ORDER BY id) AS rids 
, * 
The FROM (
SELECT id, SFZH, 'A' AS flag FROM uf_czssmz 
UNION ALL 
SELECT id, SFZH, 'B' AS flag FROM uf_czssmz_dt1 
) AS t 
) AS t 
WHERE t.r id=1