SELECT LCBH FROM formtable_main_203 where REQUESTID IN (SELECT REQUESTID FROM workflow_requestoperatelog WHERE OPERATORID = '65759' AND OPERATECODE = '5') union SELECT LCBH FROM formtable_main_419 where REQUESTID IN (SELECT REQUESTID FROM workflow_requestoperatelog WHERE OPERATORID = '65759' AND OPERATECODE = '5') 优化此sql

可以尝试将子查询改为使用 JOIN 操作，避免使用子查询：

SELECT LCBH 
FROM (
  SELECT REQUESTID, LCBH 
  FROM formtable_main_203 
  UNION 
  SELECT REQUESTID, LCBH 
  FROM formtable_main_419
) t1 
JOIN workflow_requestoperatelog t2 ON t1.REQUESTID = t2.REQUESTID 
WHERE t2.OPERATORID = '65759' AND t2.OPERATECODE = '5'

此外，如果需要加速查询，可以考虑对操作日志表 workflow_requestoperatelog 的 OPERATORID 和 OPERATECODE 字段加上索引。