如何使用和不使用group by有效地执行两个查询联合

-- 第一个查询
SELECT column1, column2, COUNT(*) as count
FROM table1
GROUP BY column1, column2

-- 第二个查询
SELECT column3, column4, COUNT(*) as count
FROM table2
GROUP BY column3, column4

-- 查询联合
SELECT column1, column2, column3, column4, count
FROM (
  SELECT column1, column2, NULL as column3, NULL as column4, count
  FROM query1
  UNION ALL
  SELECT NULL as column1, NULL as column2, column3, column4, count
  FROM query2
) AS result

-- 第一个查询
SELECT column1, column2, column3
FROM table1

-- 第二个查询
SELECT column4, column5, column6
FROM table2

-- 查询联合
SELECT column1, column2, column3
FROM (
  SELECT column1, column2, column3
  FROM table1
) AS result1
UNION ALL
SELECT column4, column5, column6
FROM (
  SELECT column4, column5, column6
  FROM table2
) AS result2