SQL测验SELECT /子查询

Question

请参阅给定的SQL语句。

1. Select SPNAME 
2. FROM SALESPERSON 
3. Where SPNUM= 
4. FROM CUSTOMER 
5. WHERE CUSTNUM=20900); 

第4行开头的子查询缺少什么？

(SELECT SPNUM
(SPNUM
(Subquery SPNUM
(FIND SPNUM

Answer 1

我认为查询应该是WHERE SPNUM = ...或WHERE SPNUM IN ...后跟子查询。为安全起见，如果子查询返回多条记录，我们可以使用WHERE SPNUM IN ...。

SELECT SPNAME
FROM SALESPERSON
WHERE SPNUM IN (SELECT SPNUM FROM CUSTOMER WHERE CUSTNUM = 20900)