Case

See Case on W3 Schools.

Syntax

CASE
  WHEN condition1 THEN result1
  WHEN condition2 THEN result2
  WHEN conditionN THEN resultN
  ELSE result
END; 

Your condition might be something like

quantity = 0

quantity > 30

Or, for a boolean, simply the variable name.

enabled
// i.e.
enabled IS TRUE

Example

Quantities

SELECT
  order_id, 
  quantity,
  CASE
    WHEN quantity > 30 THEN 'The quantity is greater than 30'
    WHEN quantity = 30 THEN 'The quantity is 30'
    ELSE 'The quantity is under 30'
  END AS quantity_text
FROM order_details; 

Boolean

Note use of NOT to reverse the boolean.

SELECT
  SUM(CASE WHEN is_supported THEN 1 ELSE 0 END) AS supported_cnt,
  SUM(CASE WHEN NOT is_supported THEN 1 ELSE 0 END) AS not_supported_cnt
FROM my_table
;