現有需求：mysql查詢特定字段，根據第一個表中某一個字段的值不同，獲取不同的表的特定字段值。
發現兩種解決方案，如有其他方法，歡迎留言補充，互相交流，共同進步~~
解決方案：
方案一：
$sql1 = "SELECT t1.id,t1.name,t1.add_time,t1.is_adopt,
CASE
WHEN t1.customer_type=2 THEN
(SELECT name FROM company_info as t2 WHERE t2.company_id=t1.customer_id)
WHEN t1.customer_type=3 THEN
(SELECT name FROM factory_info as t2 WHERE t2.factory_id=t1.customer_id)
END AS company_name,
CASE
WHEN t1.customer_type=2 THEN '經銷商'
WHEN t1.customer_type=3 THEN '廠商'
END AS company_type
FROM brand as t1 order by t1.add_time desc,t1.is_adopt asc;";
方案二：
$sql3 = "select d.id,d.name,d.add_time,d.is_adopt,
(case
when d.customer_type = 2 then
a.name
when d.customer_type = 3 then
b.name
end) AS company_name,
(CASE
WHEN d.customer_type = 2 THEN '經銷商'
WHEN d.customer_type = 3 THEN '廠商'
END) AS customer_type
from brand as d
left join company_info as a
on a.company_id=d.customer_id
left join factory_info as b
on b.factory_id=d.customer_id
order by d.add_time desc,d.is_adopt asc;";
總結一下，一種是在查詢字段時直接設置子查詢；另一種是先設置字段，在后面通過左連接的形式關聯表去查詢。
兩種方法均可實現。