Is there any difference between the different ways of giving an alias name to a table?

Question

I have a table called "Employee" with a column name called "EmployeeName" and I know that all of these different queries will give all the employees in a table:

select EmployeeName from Employee;

select EmployeeName from Employee allEmployees;

select allEmployees.EmployeeName from Employee allEmployees;

select EmployeeName from Employee as allEmployees;

They both bring up all the employees in the table, is the difference between them in terms of query efficiency or running time?

I assume that for simple queries like this, there wouldn't be much difference, but if the above were part of some much longer query, would there be a better one to use? If so, why?

Answer 1

您使用somerandomword作为表别名，这两个查询之间没有区别，它们的输出相同，因为只有一个表 ，但是如果您有两个具有相同列名的不同表，那么这将不起作用，因为存在名称冲突，时间，您必须使用别名或表名。

Answer 2

Aliases are used to give a temporary name to database table OR a column in a table. These are created to make column names more readable.

Wiki

SELECT somerandomword.EmployeeName from Employee somerandomword;
                                                 --------------
                                                   ^This is the alias name for your table

Its safer to get data from columns, especially when we use multiple tables in SELECT query, like below syntax

Syntax :

SELECT t1.col1, t2.col1 from Table_Name1 as t1, Table_Name2 as t2;

Sample Code