PostgreSQL: Add condition in where clause using CASE - postgresql

Question

I am using PostgreSQL 8.2 and I am also new to PostgreSQL.
I have to add one condition in the WHERE clause depending upon specific value (49) of the field (activity.type). Here is my Query:
SELECT activity.*
FROM activity
LEFT JOIN event_types ON activity.customstatusid = event_types.id, getviewableemployees(3222, NULL) AS report
WHERE
(
CASE WHEN activity.type = 49 THEN
'activity.individualid IN(SELECT individualid from prospects where prospects.individualid = activity.individualid)'
ELSE 1
END
)
AND activity.date BETWEEN '2016-10-01' AND '2016-10-06'
AND activity.type IN (21, 22, 49, 50, 37, 199)
AND (event_types.status = 1 or event_types.status IS NULL);
When I run above query in the command line access of PGSQL then I get below error:
ERROR: invalid input syntax for integer: "activity.individualid IN(SELECT individualid from prospects where prospects.individualid = activity.individualid)"
What I am missing here?

Answer 1

Implement your where clause as:
WHERE (
activity.type != 49 OR
activity.individualid IN (
SELECT individualid from prospects
WHERE prospects.individualid = activity.individualid)
)
AND activity.date BETWEEN '2016-10-01' AND '2016-10-06'
AND activity.type IN (21, 22, 49, 50, 37, 199)
AND (event_types.status = 1 or event_types.status IS NULL);
The first clause will only be true when either:
activity.type != 49; or
activity.type == 49 and activity.individualid is found in the subquery.