无法绑定多部分标识符的原因

Question

error - The multi-part identifier "Grant.EmpID" could not be bound.

query -

select emp.EmpID, 
COUNT(*) as CountRecords,
COUNT(GrantName) AS CountValues
From Employee as emp full join [Grant] as gr
on emp.EmpID = [Grant].EmpID 
-- This is the cause for the error ! Change it to gr.EmpID
group by emp.EmpID

Why does this error occur ? Can't I call a person by real name and also by nickname ?

Answer 1

You're aliasing [Grant] . In other words, you're stating that from here on out, [Grant] will be referred to as gr .

Use the ALIAS in the GROUP BY clause, not the tableName.

SELECT emp.EmpID, 
       COUNT(*) as CountRecords,
       COUNT(GrantName) AS CountValues
FROM   Employee as emp 
       FULL JOIN [Grant] as gr
          on emp.EmpID = gr.EmpID  -- use the alias.
GROUP BY gr.EmpID                  -- use the alias.

here's the SQL Order of Operation

• FROM clause
• WHERE clause
• GROUP BY clause
• HAVING clause
• SELECT clause
• ORDER BY clause

Answer 2

No you can't because sql server is not a human. imagine we have an Employee table which references itself

select * 
from Employee Emp, Employee Mng
where Emp.ManagerID = Mng.EmployeeID

Mng and Emp are two instances of Employee

so if I select

select * from Employee e, Employee

it will return all employee TWO times, because I am telling give me employees once under the name Employee once under the name e (alias)