SQL测验选择/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); 

在第4行开头的子查询中缺少什么？

(SELECT SPNUM 
(SPNUM 
(Subquery SPNUM 
(FIND SPNUM 

Answer 1

我想查询应该是WHERE SPNUM = ...或WHERE SPNUM IN ...后跟一个子查询。为了安全起见，我们可以在子查询返回多条记录的情况下使用WHERE SPNUM IN ...。

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