ORACLE_ALIAS

Oracle / PLSQL: ALIASES

website：https://www.techonthenet.com/oracle/alias.php

This Oracle tutorial explains how to use Oracle ALIASES (temporary names for columns or tables) with syntax and examples.

Description

Oracle ALIASES can be used to create a temporary name for columns or tables.

• COLUMN ALIASES are used to make column headings in your result set easier to read.
• TABLE ALIASES are used to shorten your SQL to make it easier to read or when you are performing a self join (ie: listing the same table more than once in the FROM clause（列出相同的表不止一次在那个from从句）).

Syntax

The syntax to ALIAS A COLUMN in Oracle/PLSQL is:

column_name AS alias_name

OR

The syntax to ALIAS A TABLE in Oracle/PLSQL is:

table_name alias_name

Parameters or Arguments

column_name

The original name of the column that you wish to alias.

table_name

The original name of the table that you wish to alias.

alias_name

The temporary name to assign.

Note

• If the alias_name contains spaces, you must enclose（包围） the alias_name in quotes（双引号）.
• if the alias_name contains number,you must enclose then alias_name in quotes.(myself addtion)
• It is acceptable to use spaces when you are aliasing a column name. However, it is not generally good practice to use spaces when you are aliasing a table name.
• The alias_name is only valid within the scope of the SQL statement.

Example - ALIAS a column

Generally, aliases are used to make the column headings in your result set easier to read. For example, when concatenating fields together(连接字段), you might alias the result.

For example:

SELECT contact_id, first_name || last_name AS NAME
FROM contacts
WHERE last_name = 'Anderson';

In this example, we've aliased the second column (ie: first_name and last_name concatenated) as NAME. As a result, NAME will display as the heading for the second column when the result set is returned. Because our alias_name did not include any spaces, we are not required to enclose the alias_name in quotes.

However, it would have been perfectly acceptable to write this example using quotes as follows:

SELECT contact_id, first_name || last_name AS "NAME"
FROM contacts
WHERE last_name = 'Anderson';

Next, let's look at an example where we are required to enclose the alias_name in quotes.

For example:

SELECT contact_id, first_name || last_name AS "CONTACT NAME"
FROM contacts
WHERE last_name = 'Anderson';

In this example, we've aliased the second column (ie: first_name and last_name concatenated) as "CONTACT NAME". Since there are spaces in this alias_name, "CONTACT NAME" must be enclosed in quotes.

Example - ALIAS a Table

When you create an alias on a table, it is either（任何一个） because you plan to list the same table name more than once in the FROM clause (ie: self join), or you want to shorten the table name to make the SQL statement shorter and easier to read.

Let's look at an example of how to alias a table name in Oracle/PLSQL.

For example:

SELECT p.product_id, p.product_name, categories.category_name
FROM products p
INNER JOIN categories
ON p.category_id = categories.category_id
ORDER BY p.product_name ASC, categories.category_name ASC;

In this example, we've created an alias for the products table called p. Now within this SQL statement, we can refer to the products table as p.

When creating table aliases, it is not necessary to create aliases for all of the tables listed in the FROM clause. You can choose to create aliases on any or all of the tables.

For example, we could modify our example above and create an alias for the categories table as well.

SELECT p.product_id, p.product_name, c.category_name
FROM products p
INNER JOIN categories c
ON p.category_id = c.category_id
ORDER BY p.product_name ASC, c.category_name ASC;

Now we have an alias for categories table called c as well as the alias for the products table called p.