If you want to add an additional column, how do you display it conditionally and calculate its value?

To add a computed column that is shown only when a condition is met, you can use a CASE expression or a computed column in the SELECT list. For example, suppose you have a table "accounts" with columns "balance" and "status". You want to show a column "overdrawn" that is 1 when balance < 0 and 0 otherwise:

SELECT

account_id,

balance,

CASE WHEN balance < 0 THEN 1 ELSE 0 END AS overdrawn

FROM accounts;

If you only want the column to appear when a specific condition holds (e.g., status = 'active'), you can wrap the CASE in a filter or use a NULL to hide it:

SELECT

account_id,

balance,

CASE WHEN status = 'active' THEN

   CASE WHEN balance < 0 THEN 1 ELSE 0 END
   ELSE NULL

END AS overdrawn

FROM accounts;

This approach keeps the column in the result set but returns NULL for rows that don't meet the outer condition. In many RDBMS you can also create a persisted computed column in the table definition, but for ad‑hoc queries the CASE method is most common.