How to create virtual column using MySQL SELECT

Question

If I do SELECT a AS b and b is not a column in the table  would query create the  virtual  column   in fact  I need to incorporate some virtual column into the query and process some information into the query so I can use it with each item later on

User · Accepted Answer

Something like   SELECT id  email  IF active   1   enabled    disabled   AS account status FROM users   This allows you to make operations and show it as columns   EDIT   you can also use joins and show operations as columns   SELECT u id  e email  IF c id IS NULL   no selected   c name  AS country FROM users u LEFT JOIN countries c ON u country id   c id

User · Answer

Try this one if you want to create a virtual column  age  within a select statement   select brand  name   10  as age from cars

User · Answer

You could use a CASE statement  like SELECT name         address         CASE WHEN a  lt  b THEN  1                ELSE  2  END AS one or two FROM

User · Answer

SELECT only retrieves data from the database  it does not change the table itself   If you write  SELECT a AS b FROM x    b  is just an alias name in the query  It does not create an extra column  Your result in the example would only contain one column named  b   But the column in the table would stay  a    b  is just another name   I don t really understand what you mean with  so I can use it with each item later on   Do you mean later in the select statement or later in your application  Perhaps you could provide some example code

User · Answer

Try this one if you want to create a virtual column  age  within a select statement   select brand  name   10  as age from cars

User · Answer

SELECT only retrieves data from the database  it does not change the table itself   If you write  SELECT a AS b FROM x    b  is just an alias name in the query  It does not create an extra column  Your result in the example would only contain one column named  b   But the column in the table would stay  a    b  is just another name   I don t really understand what you mean with  so I can use it with each item later on   Do you mean later in the select statement or later in your application  Perhaps you could provide some example code

User · Answer

You can add virtual columns as  SELECT  1  as temp   But if you tries to put where condition to additionally generated column  it wont work and will show an error message as the column doesn t exist    We can solve this issue by returning sql result as a table ie   SELECT tb   from  SELECT 1 as temp  as tb WHERE tb temp   1

User · Answer

Your syntax would create an alias for a as b  but it wouldn t have scope beyond the results of the statement  It sounds like you may want to create a VIEW

User · Answer

You could use a CASE statement  like SELECT name         address         CASE WHEN a  lt  b THEN  1                ELSE  2  END AS one or two FROM

User · Answer

SELECT only retrieves data from the database  it does not change the table itself   If you write  SELECT a AS b FROM x    b  is just an alias name in the query  It does not create an extra column  Your result in the example would only contain one column named  b   But the column in the table would stay  a    b  is just another name   I don t really understand what you mean with  so I can use it with each item later on   Do you mean later in the select statement or later in your application  Perhaps you could provide some example code

User · Answer

Your syntax would create an alias for a as b  but it wouldn t have scope beyond the results of the statement  It sounds like you may want to create a VIEW

User · Answer

SELECT only retrieves data from the database  it does not change the table itself   If you write  SELECT a AS b FROM x    b  is just an alias name in the query  It does not create an extra column  Your result in the example would only contain one column named  b   But the column in the table would stay  a    b  is just another name   I don t really understand what you mean with  so I can use it with each item later on   Do you mean later in the select statement or later in your application  Perhaps you could provide some example code

User · Answer

Your syntax would create an alias for a as b  but it wouldn t have scope beyond the results of the statement  It sounds like you may want to create a VIEW

User · Answer

You can add virtual columns as  SELECT  1  as temp   But if you tries to put where condition to additionally generated column  it wont work and will show an error message as the column doesn t exist    We can solve this issue by returning sql result as a table ie   SELECT tb   from  SELECT 1 as temp  as tb WHERE tb temp   1

User · Answer

Your syntax would create an alias for a as b  but it wouldn t have scope beyond the results of the statement  It sounds like you may want to create a VIEW

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