Firebird and stored procedures: if exists then else - stored-procedures

Question

I'm trying to create a stored procedure for firebird 2.1 (this is the version which is to be used)
But am getting a bit stuck, so any help is appreciated.
The final version should compare 4 values agains the table, and retreive either the primaryid if the value exists, or create the new entry in the table, and return the new primaryid.
But I get stuck with only one value lookup, and it's not even using the variable yet.
SET TERM ^ ;
CREATE PROCEDURE TESTSP
( A Varchar(64) )
RETURNS
( RESULT Integer )
AS
BEGIN
IF (EXISTS (SELECT PRIMARYID FROM TABLENAME WHERE FIELD = 'Some string')) then
SELECT PRIMARYID FROM TABLENAME WHERE FIELD = 'Some string' into :primaryid;
result = PRIMARYID;
ELSE
INSERT INTO TABLENAME (FIELD) VALUES ('Some string');
result = gen_id(GEN_TABLEID, 0);
END^
SET TERM ; ^
I get a "Token unknown" for the Else command.
Update after responses:
Now I want to use the 4 variables and return the 4 results.
I think I need a for loop to do so, but with firebird, the for function means something else.
So what would be the way to go?
SET TERM ^ ;
CREATE PROCEDURE TESTSP
( value1 Varchar(64) )
RETURNS
( RESULT1 Integer )
AS
BEGIN
IF (EXISTS (SELECT PRIMARYID FROM TABLENAME WHERE FIELD = :value1)) then
SELECT PRIMARYID FROM TABLENAME WHERE FIELD = value1 into :result1;
ELSE BEGIN
result1 = gen_id(GEN_TABLEID, 1);
INSERT INTO TABLENAME (PRIMARYID, FIELD) VALUES (:result1, :value1);
END
suspend;
END^
SET TERM ; ^

Answer 1

As Tico already answered you have to use begin / end to group multiple statements in then / else part. The error abut column PRIMARYID being unknown is because you reference to it without having declared a local variable for it. Try this:
CREATE PROCEDURE TESTSP ( A Varchar(64) )
RETURNS ( RESULT Integer )
AS
BEGIN
-- initialize the result
Result = NULL;
-- check is the string already in table
SELECT PRIMARYID FROM TABLENAME WHERE FIELD = 'Some string' into :Result;
IF (Result is NULL) then
INSERT INTO TABLENAME(PRIMARYID, FIELD) VALUES(gen_id(GEN_TABLEID, 1), 'Some string') RETURNING PRIMARYID INTO :Result;
END^

Answer 2

I think your stored procedure should look like this:
SET TERM ^ ;
CREATE PROCEDURE TESTSP
( A Varchar(64) )
RETURNS ( result Integer )
AS
BEGIN
IF (EXISTS (SELECT PRIMARYID
FROM TABLENAME
WHERE FIELD = 'Some string')) then
SELECT PRIMARYID
FROM TABLENAME
WHERE FIELD = 'Some string'
into :result;
ELSE BEGIN
result = gen_id(GEN_TABLEID, 1);
INSERT INTO TABLENAME
(PRIMARYID, FIELD)
VALUES (:result, 'Some string');
END
END^
SET TERM ; ^

Answer 3

If you have multiple instruction for then and/ or else clause you must use BEGIN ... END-block!
SET TERM ^ ;
CREATE PROCEDURE TESTSP
( A Varchar(64) )
RETURNS
( RESULT Integer )
AS
BEGIN
IF (EXISTS (SELECT PRIMARYID FROM TABLENAME WHERE FIELD = 'Some string')) then
BEGIN
SELECT PRIMARYID FROM TABLENAME WHERE FIELD = 'Some string' into :primaryid;
result = PRIMARYID;
END
ELSE
BEGIN
INSERT INTO TABLENAME (FIELD) VALUES ('Some string');
result = gen_id(GEN_TABLEID, 0);
END
END^
SET TERM ; ^