mysql - 如何选择其他查询中不存在的数据

Question

我正在尝试从表数据中进行选择，但我希望结果不存在于此选择中。

(SELECT * FROM data WHERE category = 'A' ORDER BY RAND() LIMIT 4)
UNION ALL
(SELECT * FROM data WHERE category = 'B' ORDER BY RAND() LIMIT 4)` 

所以没有行被双选。
摆弄sample data .

Answer 1

不存在:

SELECT * FROM table1 t1
WHERE NOT EXISTS (
  SELECT 1 FROM (
    (SELECT * FROM table1 WHERE category = 'A' ORDER BY RAND() LIMIT 4)
    UNION ALL
    (SELECT * FROM table1 WHERE category = 'B' ORDER BY RAND() LIMIT 4)
  ) t 
  WHERE t.id = t1.id AND t.category = t1.category  
)

参见 demo .