Question

我正在尝试将子查询的结果插入到表中，但我要插入的表具有唯一的主ID。我想取EID编号的最大值，并在我试图插入表格的任何条目中加1。

表格我要插入：

----------------------------------------------------
EID (pk)     |     First Name       | Employment Date
----------------------------------------------------
   1         |     John             |      2016-01-01
   2         |     Joe              |      2013-01-01
   3         |     Jill             |      2012-01-01
   4         |     Jen              |      2017-01-01

我的子查询声明：

(SELECT FIRSTNAME, ORDERDATE as EMPLOYMENTDATE
  FROM CUSTOMER, ORDER
WHERE CUSTOMER.id = ORDER.id
AND ORDERDATE >= DATE '2017-01-01')

问题是插入，因为我没有唯一的ID来生成。这是在SQL Server上

我想插入这样的东西：

INSERT INTO EMPLOYEE(EID, FIRSTNAME, EMPLOYMENTDATE)
SELECT ??????WHAT GOES HERE??????, FIRSTNAME, ORDERDATE as EMPLOYMENTDATE
  FROM CUSTOMER, ORDER
WHERE CUSTOMER.id = ORDER.id
AND ORDERDATE >= DATE '2017-01-01'

Answer 1

假设EID是身份，这就是：

INSERT INTO EMPLOYEE(FIRSTNAME, EMPLOYMENTDATE)
SELECT  FIRSTNAME, ORDERDATE as EMPLOYMENTDATE
  FROM CUSTOMER, ORDER
WHERE CUSTOMER.id = ORDER.id
AND ORDERDATE >= DATE '2017-01-01'

Answer 2

你是对的，因为你正在使用子查询，它会是这样的：

INSERT INTO EMPLOYEE(EID, FIRSTNAME, EMPLOYMENTDATE)
SELECT 
    ISNULL((MAX(Emp.EID)+1),1) AS EID,
    CustOrd.FirstName,
    CustOrd.EmploymentDate
FROM 
    EMPLOYEE Emp,
    (SELECT FIRSTNAME, ORDERDATE as EMPLOYMENTDATE
     FROM CUSTOMER, ORDER
     WHERE CUSTOMER.id = ORDER.id
     AND ORDERDATE >= DATE '2017-01-01') CustOrd

从SQL子查询生成唯一ID

2 个答案: