select * from 商品表B b where  not exists 
(select 1 from 销售表C c where b.goods=c.goods)

------解决方案--------------------
SQL code

CREATE TABLE 客户表A
(
 customer VARCHAR(10)
 )
 
 INSERT INTO 客户表A
SELECT '张三' UNION
SELECT '李四' UNION
SELECT '王二麻子'


CREATE TABLE 商品表B
(
  goods VARCHAR(10)
  )
  
  INSERT INTO 商品表B
SELECT '商品1' UNION
SELECT '商品2' UNION
SELECT '商品3' UNION
SELECT '商品4'


CREATE TABLE 销售表C
( customer  VARCHAR(10),
  goods VARCHAR(10)
  )
  
  INSERT INTO 销售表C
SELECT '张三', '商品1' UNION
SELECT '张三', '商品4' UNION
SELECT '李四', '商品2' UNION
SELECT '王二麻子', '商品3' UNION
SELECT '王二麻子', '商品1'

SELECT A.customer,B.goods
FROM 客户表A AS A,商品表B AS B
WHERE goods NOT IN (SELECT goods FROM 销售表C WHERE A.customer = 销售表C.customer)

------解决方案--------------------
[引用:]
SQL code

select * from 商品表B b where  not exists 
(select 1 from 销售表C c where b.goods=c.goods)