PostgreSQL if else syntax error - postgresql

Question

i try a query that runs on mssql however does not run postgreSQL...
SQL Query is..
IF EXISTS (SELECT * FROM Kategoriler WHERE KategoriId = 119)
BEGIN
SELECT * FROM Kategoriler
END
ELSE
SELECT * FROM Adminler
i searched it and i found in stackoverflow
DO
$BODY$
BEGIN
IF EXISTS (SELECT 1 FROM orders) THEN
DELETE from orders;
ELSE
INSERT INTO orders VALUES (1,2,3);
END IF;
END;
$BODY$
but i do not want to use DO or, $body etc... I do not want to write any function or other etc...
i want to write only if else statement in postgreSQL... Please help me...

Answer 1

T-SQL supports some procedural statement like IF. PostgreSQL doesn't support it, so you cannot rewrite your query to postgres simply. Sometime you can use Igor's solution, sometime you can use plpgsql (functions) and sometime you have to modify your application and move procedural code from server to client.

Answer 2

Try something like
SELECT *
FROM Kategoriler
UNION ALL
SELECT *
FROM Adminler
WHERE NOT EXIST (SELECT * FROM Kategoriler WHERE KategoriId = 119)
Will only work if Kategoriler and Adminler have same structure. Otherwise you need to specify list of fields instead of *

Answer 3

In my case I needed to know if a record existed.
I had to write a function
CREATE OR REPLACE FUNCTION public.pro_device_exists(vdn character varying)
RETURNS boolean
LANGUAGE plpgsql
AS $function$
BEGIN
IF EXISTS (SELECT 1 FROM tags WHERE device_name = upper(vdn)) THEN
return true;
ELSE
return false;
END IF;
END; $function$
Then I was able to call this function in my code ... just a portion of my code
if pro_device_exists(vdn) then
update tags
set device_id = 11 where device_id = pro_device_id(vdn) and tag_type=10;
update tags
set device_id = pro_device_id(vdn) where tag_id = vtag_id;
vmsg = (select 'Device Now set to ' || first_name || ' ' || last_name from tags where tag_id=vtag_id);
vaction = 'Refresh Device Data';
else
vmsg = 'Device is not registered on this system';
vaction = 'No Nothing';
end if;