嗨,大家好,我只是寫了2個查詢這給了我同樣的結果,我想問問你,如果它是重要的,我把它寫:做它無論我怎樣寫我的SQL查詢(如果正確)
1)
select First_Name, monthly_discount, pack_id, main_phone_num
from customers
where pack_id in(select p.pack_id
from packages p JOIN sectors s
on s.sector_id = p.sector_id where s.sector_name = 'business')
2)
SELECT first_name , monthly_discount , pack_id , main_phone_num ,
secondary_phone_num
FROM customers
WHERE pack_id IN
(SELECT pack_id
FROM packages
WHERE sector_id IN
( SELECT sector_id
FROM sectors
WHERE sector_name = 'Business'))
哪'RDBMS'您使用。我可能會用'EXISTS/JOIN'組合 –