SQL | Aliases

09 Jan, 2019
Aliases are the temporary names given to table or column for the purpose of a particular SQL query. It is used when name of column or table is used other than their original names, but the modified name is only temporary.
Aliases are created to make table or column names more readable.
The renaming is just a temporary change and table name does not change in the original database.
Aliases are useful when table or column names are big or not very readable.
These are preferred when there are more than one table involved in a query.
Basic Syntax:
For column alias:SELECT column as alias_name FROM table_name;
column: fields in the table
alias_name: temporary alias name to be used in replacement of original column name 
table_name: name of table

SELECT column as alias_name FROM table_name;
column: fields in the table
alias_name: temporary alias name to be used in replacement of original column name 
table_name: name of table

For table alias:SELECT column FROM table_name as alias_name;
column: fields in the table 
table_name: name of table
alias_name: temporary alias name to be used in replacement of original table name

SELECT column FROM table_name as alias_name;
column: fields in the table 
table_name: name of table
alias_name: temporary alias name to be used in replacement of original table name

Queries for illustrating column alias
To fetch ROLL_NO from Student table using CODE as alias name.SELECT ROLL_NO AS CODE FROM Student; 
Output:CODE1234
To fetch ROLL_NO from Student table using CODE as alias name.SELECT ROLL_NO AS CODE FROM Student; 
Output:CODE1234
To fetch ROLL_NO from Student table using CODE as alias name.SELECT ROLL_NO AS CODE FROM Student; 
Output:CODE1234
To fetch ROLL_NO from Student table using CODE as alias name.SELECT ROLL_NO AS CODE FROM Student; 
Output:CODE1234
SELECT ROLL_NO AS CODE FROM Student; 

Output:
 
To fetch Branch using Stream as alias name and Grade as CGPA from table Student_Details.SELECT Branch AS Stream,Grade as CGPA FROM Student_Details; 
Output:StreamCGPAInformation TechnologyOComputer ScienceEComputer ScienceOMechanical EngineeringA
To fetch Branch using Stream as alias name and Grade as CGPA from table Student_Details.SELECT Branch AS Stream,Grade as CGPA FROM Student_Details; 
Output:StreamCGPAInformation TechnologyOComputer ScienceEComputer ScienceOMechanical EngineeringA
To fetch Branch using Stream as alias name and Grade as CGPA from table Student_Details.SELECT Branch AS Stream,Grade as CGPA FROM Student_Details; 
Output:StreamCGPAInformation TechnologyOComputer ScienceEComputer ScienceOMechanical EngineeringA
SELECT Branch AS Stream,Grade as CGPA FROM Student_Details; 

Output:
Queries for illustrating table alias
Generally table aliases are used to fetch the data from more than just single table and connect them through the field relations.
To fetch Grade and NAME of Student with Age = 20.SELECT s.NAME, d.Grade FROM Student AS s, Student_Details
AS d WHERE s.Age=20 AND s.ROLL_NO=d.ROLL_NO; 
Output:NAMEGradeSUJITO
To fetch Grade and NAME of Student with Age = 20.SELECT s.NAME, d.Grade FROM Student AS s, Student_Details
AS d WHERE s.Age=20 AND s.ROLL_NO=d.ROLL_NO; 
Output:NAMEGradeSUJITO
To fetch Grade and NAME of Student with Age = 20.SELECT s.NAME, d.Grade FROM Student AS s, Student_Details
AS d WHERE s.Age=20 AND s.ROLL_NO=d.ROLL_NO; 
Output:NAMEGradeSUJITO
To fetch Grade and NAME of Student with Age = 20.SELECT s.NAME, d.Grade FROM Student AS s, Student_Details
AS d WHERE s.Age=20 AND s.ROLL_NO=d.ROLL_NO; 
Output:NAMEGradeSUJITO
SELECT s.NAME, d.Grade FROM Student AS s, Student_Details
AS d WHERE s.Age=20 AND s.ROLL_NO=d.ROLL_NO; 

Output:
 
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