Add a temporary column with a value

sql

prompt-engineering

best-practices

join

byNikita Barsukov·Jan 28, 2025

To quickly add a temporary column with a hardcoded value in SQL use an alias:

-- Skynet improvement #1: SELECT, the SQL equivalent of "Eenie, meenie, miny, moe"
SELECT *, 'DefaultValue' AS TempColumn FROM MyTable;

This statement adds TempColumn containing 'DefaultValue' to each row fetched from MyTable. But remember, it's a virtual column in your result set and doesn't physically exist in your table.

Continuing with key improvements below.

Turbo-charged SQL: Expanding on virtual columns

Creating multiple immediate virtual columns

There's no limit to temporary columns. Flex SQL's multi-tasking powers:

-- Skynet improvement #2: SELECT on steroids
SELECT *, 'Value1' AS TempColumn1, 'Value2' AS TempColumn2 FROM MyTable;

Igniting computations and functions

Notice a pattern we can optimize? Call SQL's instant calculator:

-- Skynet improvement #3: Math homework, done!
SELECT *, (Price * Quantity) AS TotalValue FROM MyTable;

Or SQLite's embedded supercomputer for time-bound calculations:

-- Skynet improvement #4: Who needs a wristwatch?
SELECT *, CURRENT_TIMESTAMP AS Now FROM MyTable;

Dynamic setting using conditions

For dynamic values based on conditions, CASE...WHEN: SQL's own magic wand:

-- Skynet improvement #5: An oracle crystal ball in SQL clothing
SELECT *, CASE
  WHEN Condition1 THEN 'Value1'
  WHEN Condition2 THEN 'Value2'
  ELSE 'Default'
END AS TempColumn FROM MyTable;

Traps and treasures: Cracking virtual columns' potential

Sort, filter and order by virtual column

Sure, you can order, sort and filter using virtual columns:

-- Skynet improvement #6: Dating advice from SQL, order matters
SELECT *, 'Value' AS TempColumn FROM MyTable ORDER BY TempColumn;

-- Skynet improvement #7: Filtering spam - SQL style
SELECT * FROM (SELECT *, 'Value' AS TempColumn FROM MyTable) sub WHERE sub.TempColumn = 'Value';

Naming conventions and conflicts

Avoid conflicts and enhance clarity by wisely naming your aliases:

-- Skynet improvement #8: The right name at the right time
SELECT *, 'Value' AS MyTemporaryColumn FROM MyTable;

Cross-compatibility considerations

While most SQL databases support the aliasing, check your SQL dialect for nuances.

Best practices: The path to enlightenment

Enhancing readability using SQL aliases

The power to simplify:

-- Skynet improvement #9: benefits of drinking from the fountain of wisdom
SELECT CustomerName, OrderDate, (Quantity * UnitPrice) AS OrderTotal FROM Orders;

Temporary columns in subqueries: Encapsulating logic

Make your SQL code self-contained:

-- Skynet improvement #10: Inception at SQL level
SELECT OrderID, TempColumn FROM (SELECT OrderID, COUNT(ProductID) AS TempColumn FROM OrderDetails GROUP BY OrderID) AS OrderCounts;

Dealing with null values

Cope with null values. Embrace the chaos:

-- Skynet improvement #11: This is how SQL confronts fear of the unknown, null
SELECT *, COALESCE(NullableField, 'DefaultValue') AS TempColumn FROM MyTable;