SQL Alias ​​Aliases

SQL aliases are used to give a table, or a column in a table, a temporary alias.

The effect is:

1, used to change the column names in the result set

2, after changing the alias, prevent name conflict, or simplify the name to make the meaning of the name more reasonable and clear.

This alias is only valid during ad hoc queries.

When creating an alias, use the AS keyword.

Create aliases for data columns:

SELECT column_name AS alias_name FROM table_name;

Create an alias for the data table:

SELECT column_name(s) FROM table_name AS alias_name;

Example:

SELECT customer_id AS ID FROM Customers;

Search results:

ID

1

2

3

4

5

Note that if you create an alias with spaces in it, use double quotes or square brackets to enclose the name.(double quotation marks or square brackets)

When aliases are usually used, we have made a certain combination of data in multiple columns, as shown below, combining address, zip code, city, and country as a new address.

SELECT CustomerName, Address + ', ' + PostalCode + ' ' + City + ', ' + Country AS Address

FROM Customers;

If it is a MySQL database:

SELECT CustomerName, CONCAT(Address,', ',PostalCode,', ',City,', ',Country) AS Address

FROM Customers;

If it is an Oracle database:

SELECT CustomerName, (Address || ', ' || PostalCode || ' ' || City || ', ' || Country) AS Address

FROM Customers;

An example of using table aliases is as follows.

SELECT o.OrderID, o.OrderDate, c.CustomerName

FROM Customers AS c, Orders AS o

WHERE c.CustomerName='Around the Horn' AND c.CustomerID=o.CustomerID;

This example uses two tables for joint query, using aliases to shorten the name of the table, which is more convenient to use.

In summary, the usage of aliases in SQL is:

1, when there are multiple tables in the query, or the same table SELF JOIN.

2, to use a function in a query, the result needs to be calculated and named as a column.

3, the column name is too long to read or type.

4, when the data of multiple columns is to be combined together.

Reference:

SQL Aliases