mysql - 如何合并两个表的结果并在sql中以单列显示

Question

我有三个表 customer1 、 customer2 和 product ，如下所示:

客户1:

c_id --- c_name
----------------
1    ---    anns

2    ---   skja

3    ---    kkjk

客户2:

c_id --- c_name
----------------
11   ---  sjhja

12   ---  skkkkk

13   ---  aaasss

产品:

p_id --- c_id ---  p_name
-------------------------
1    ---   1  ---   pen

2    ---   2  ---  card

3    ---   3  ---   cell

4    ---   11  ---  pot

5    ---   12  ---  ice

6    ---   13  ---  apple

我想将 product 表中 c_id 的值替换为 customer1 和 中的 c_name客户2

我正在使用下面的sql查询:

SELECT c1.c_name or c2.c_name as customer_name, p.p_name from product p
left JOIN customer1 c1 on c1.c_id=p.c_id
left JOIN customer2 c2 on c2.c_id=p.c_id;

得到结果:

c_name -----  p_name
---------------
null   -----  pen

null   -----  card 

null   -----  cell

null   -----  pot

null   -----  ice

null   -----  apple

期望的结果:

c_name -----  p_name
----------------------
anns    ----- pen

skja    ----- card 

kkjk    ----- cell

sjhja   ----- pot

skkkkk  ----- ice

aaasss  ----- apple

请帮助我获得想要的结果。

Answer 1

SELECT coalesce(c1.c_name,c2.c_name) as cus_name, p.p_name product_name 
from   product p
JOIN   customer1 c1 
on     c1.c_id=p.c_id
JOIN   customer2 c2 
on     c2.c_id=p.c_id;