mysql - MYSQL 查询：组合列并获取计数

Question

我有大约 9 个包含相同类型字段的表。我想首先组合其中的 9 个，然后在该组合列中获得唯一值的不同计数。这是我到目前为止尝试过的，但无济于事。我也不确定这是返回此值的最有效方法吗？

SELECT COUNT(DISTINCT aircraft_id) FROM 
(
SELECT aircraft_id FROM database.a_message UNION ALL
SELECT aircraft_id FROM database.b_message UNION ALL
SELECT aircraft_id FROM database.c_message UNION ALL
SELECT aircraft_id FROM database.d_message UNION ALL
SELECT aircraft_id FROM database.e_message UNION ALL
SELECT aircraft_id FROM database.f_message UNION ALL
SELECT aircraft_id FROM database.g_message UNION ALL
SELECT aircraft_id FROM database.h_message UNION ALL
SELECT aircraft_id FROM database.i_message
) ;

Answer 1

SELECT DISTINCT aircraft_id,count(aircraft_id) FROM 
(
SELECT aircraft_id FROM database.a_message UNION ALL
SELECT aircraft_id FROM database.b_message UNION ALL
SELECT aircraft_id FROM database.c_message UNION ALL
SELECT aircraft_id FROM database.d_message UNION ALL
SELECT aircraft_id FROM database.e_message UNION ALL
SELECT aircraft_id FROM database.f_message UNION ALL
SELECT aircraft_id FROM database.g_message UNION ALL
SELECT aircraft_id FROM database.h_message UNION ALL
SELECT aircraft_id FROM database.i_message
) group by aircraft_id;

或者

select aircraft_id,count(aircraft_id)
(
SELECT DISTINCT aircraft_id FROM 
(
SELECT aircraft_id FROM database.a_message UNION ALL
SELECT aircraft_id FROM database.b_message UNION ALL
SELECT aircraft_id FROM database.c_message UNION ALL
SELECT aircraft_id FROM database.d_message UNION ALL
SELECT aircraft_id FROM database.e_message UNION ALL
SELECT aircraft_id FROM database.f_message UNION ALL
SELECT aircraft_id FROM database.g_message UNION ALL
SELECT aircraft_id FROM database.h_message UNION ALL
SELECT aircraft_id FROM database.i_message
)
) group by aircraft_id;