AWS Redshift IF-ELSE Logic

Question

I basically want to do the following thing in Redshift but since Redshift does not support procedural statements I am unsure how to achieve my goal:

IF EXISTS (select username,accountnumber from table where username={1})
THEN
    IF {0} NOT IN accountnumber 
        update table set accountnumber = 
        accountnumber+=',{0}' where username='{1}'
    END IF
ELSE
    insert into table values({1},{0});
END IF

With param 1 being a user id and param 2 being a username

What would be the best way to achieve this in redshift? Thanks for any help in advance

Running:

CREATE TABLE IF NOT EXISTS table (account_number 
varchar(100), username varchar(50));
case when true
update table set accountnumber = accountnumber+=',{0}' 
where username='{1}'
else insert into table values ('{0}','{1}')
end

defining true is just for demo purposes. I am getting the following error:

---> syntax error at or near "case"
LINE 2: case when 1=1

Answer 1

I see that redshift supports exists so maybe this will work

/* if the row is there it'll update it. If not it won't */
UPDATE Table Set Field='NewValue' Where KeyValue=1

/* if the row is not there it'll insert it */
INSERT INTO Table (KeyValue,Field1,Field2)
SELECT 1,'NewValue','NewValue'
WHERE NOT EXISTS (SELECT * FROM Table WHERE KeyValue=1)

Answer 2

You need to use CASE expression which works similarly to if-else .

case when new_record = existing_record
update existing_record
else insert new_record
end

Answer 3

If I'm not mistaken, it seems like you are trying to do an upsert. You can make use of merge functionality on redshift? You will need to use a temporary table for holding some of the values before you do the insert/update.

Here are some examples from redshift documentation

https://docs.aws.amazon.com/redshift/latest/dg/merge-examples.html