SQLServer中的错误：子查询返回的值超过1

Question

我想从两个不同的表（姓氏和名称）向客户端插入表数据。此外，我想有一个第三栏（电子邮件），从前两个连接。当我尝试下面的代码时，它给了我以下错误：“子查询返回多个值”。

insert into CLIENTS (LastName,Firstname, EMAIL) 
select (select top 150 Surname from Surname order by NEWID()), 
    (select top 150 Name from Name order by Newid()), 
    (select concat(concat(FisrtName, LastName),'@novaims.com') from clients); 

您能否帮我理解问题在哪里？

Answer 1

您需要将表格引用移至from子句。我想这你想要做什么：

insert into CLIENTS (LastName, Firstname, EMAIL) 
    select surname, name, concat(name, surname, '@novaims.com') 
    from (select Surname, row_number() over (order by newid()) as seqnum 
      from Surname 
     ) s join 
     (select Name, row_number() over (order by newid()) as seqnum 
      from Name 
     ) 
     on n.seqnum = s.seqnum; 

另一种方法是使用apply：

insert into CLIENTS (LastName, Firstname, EMAIL) 
    select top 150 s.surname, n.name, concat(n.name, s.surname, '@novaims.com') 
    from surname s cross apply 
     (select top 1 n.* 
      from names n 
      order by newid() 
     ) n 
    order by newid(); 

这更类似于原来的想法。但请注意，同名可能会出现多次。对于第一个版本，性能应该更好（因为排序只在每个表上发生一次）。

Answer 2

错误消息很明显，您的子查询可能会导致多个记录。试试这个

;WITH cte 
    AS (SELECT 1 AS val 
     UNION ALL 
     SELECT val + 1 
     FROM cte 
     WHERE val < 150) 
SELECT FisrtName, 
     LastName, 
     Concat(FisrtName, LastName, '@novaims.com') 
FROM cte 
     OUTER apply (SELECT TOP 1 Surname FROM Surname ORDER BY Newid()) s (FisrtName) 
     OUTER apply (SELECT TOP 1 NAME FROM NAME ORDER BY Newid()) n (LastName) 
    Option (Maxrecursion 0)