Error -206 creating Interbase stored procedure - stored-procedures

Question

I am attempting to create a stored procedure using an IBConsole interactive SQL window. The intent of the procedure is to gather data from two tables, do some processing on that data, insert rows containing that data into a working table, then return the rows from the working table as the stored procedure result. The stored procedure:
SET TERM ^;
CREATE PROCEDURE BIBLIO_SUBJECT
RETURNS (ID INTEGER, SUBJECT VARCHAR(200))
AS
DECLARE VARIABLE CUR_SUBJECT VARCHAR(200);
DECLARE VARIABLE SUBJECT_LIST VARCHAR(500);
DECLARE VARIABLE BIBLIOID INTEGER;
DECLARE VARIABLE NEXTPOS INTEGER;
BEGIN
DELETE FROM TSUBJECTS;
FOR SELECT BIBLIO.ID, BIBLIO.SUBJECTS
FROM BIBLIO
WHERE BIBLIO.PUBLISH = TRUE
INTO :BIBLIOID, :SUBJECT_LIST
DO
BEGIN
SUBJECT_LIST = BIBLIO.SUBJECTS + ';';
NEXTPOS = LOCATE(";", SUBJECT_LIST);
WHILE (:NEXTPOS > 1) DO
BEGIN
CUR_SUBJECT = SUBSTR(:SUBJECT_LIST, 1, NEXTPOS - 1);
SUBJECT_LIST = SUBSTR(:SUBJECT_LIST, NEXTPOS + 1, STRLEN(SUBJECT_LIST));
INSERT INTO TSUBJECTS (SUBJECT, ID) VALUES(:CUR_SUBJECT, :BIBLIOID);
NEXTPOS = LOCATE(";", SUBJECT_LIST);
END
END
FOR SELECT BIBLIO_BEAST.BIBLIO_ID, BEAST.BEAST_NAME
FROM BIBLIO_BEAST
INNER JOIN BEAST ON (BEAST.ID = BIBLIO_BEAST.BEAST_ID)
INNER JOIN BIBLIO ON (BIBLIO.ID = BIBLIO_BEAST.BIBLIO_ID)
WHERE BIBLIO.PUBLISH = TRUE
INTO :BIBLIOID, :CUR_SUBJECT
DO
BEGIN
INSERT INTO TSUBJECTS (SUBJECT, ID) VALUES(:CUR_SUBJECT, :BIBLIOID);
END
FOR SELECT ID, SUBJECT
FROM TSUBJECTS
INTO :ID, :SUBJECT
DO
SUSPEND;
END^
SET TERM ;^
When I execute the above code in IBConsole I get the error:
Error at line 2
Dynamic SQL Error
SQL error code = -206
Column unknown
SQL - CREATE PROCEDURE BIBLIO_SUBJECT
RETURNS (ID INTEGER, SUBJECT VARCHAR(200))
AS
DECLARE VARIABLE CUR_SUBJECT VARCHAR(200);
DECLARE VARIABLE SUBJECT_LIST VARCHAR(500);
DECLARE VARIABLE BIBLIOID INTEGER;
DECLARE VARIABLE NEXTPOS INTEGER;
BEGIN
DELETE FROM TSUBJECTS;
FOR SELECT BIBLIO.ID, BIBLIO.SUBJECTS
FROM BIBLIO
WHERE BIBLIO.PUBLISH = TRUE
INTO :BIBLIOID, :SUBJECT_LIST
DO
BEGIN
SUBJECT_LIST = BIBLIO.SUBJECTS + ';';
NEXTPOS = LOCATE(";", SUBJECT_LIST);
WHILE (:NEXTPOS > 1) DO
BEGIN
CUR_SUBJECT = SUBSTR(:SUBJECT_LIST, 1, NEXTPOS - 1);
SUBJECT_LIST = SUBSTR(:SUBJECT_LIST, NEXTPOS + 1, STRLEN(SUBJECT_LIST));
INSERT INTO TSUBJECTS (SUBJECT, ID) VALUES(:CUR_SUBJECT, :BIBLIOID);
NEXTPOS = LOCATE(";", SUBJECT_LIST);
END
END
FOR SELECT BIBLIO_BEAST.BIBLIO_ID, BEAST.BEAST_NAME
FROM BIBLIO_BEAST
INNER JOIN BEAST ON (BEAST.ID = BIBLIO_BEAST.BEAST_ID)
INNER JOIN BIBLIO ON (BIBLIO.ID = BIBLIO_BEAST.BIBLIO_ID)
WHERE BIBLIO.PUBLISH = TRUE
INTO :BIBLIOID, :CUR_SUBJECT
DO
BEGIN
INSERT INTO TSUBJECTS (SUBJECT, ID) VALUES(:CUR_SUBJECT, :BIBLIOID);
END
FOR SELECT ID, SUBJECT
FROM TSUBJECTS
INTO :ID, :SUBJECT
DO
SUSPEND;
END
It doesn't say which column is "unknown", and line 2 is (apparently) the RETURNS clause of the CREATE PROCEDURE. Not at all helpful.
Each of the SQL statements in the stored procedure (3 SELECTs, a DELETE, 2 INSERTs) work without error if executed separately in an Interactive SQL window, so all of their columns are "known". BIBLIO_SUBJECT is not the name of an existing stored procedure, nor is it the name of an existing table, or anything else in the database.
This has me baffled. Online searches provide no answer. So I am hoping the clever Stack Overflow people can help me get this working.
David

Answer 1

Well, I figured it out. It was the statement:
SUBJECT_LIST = BIBLIO.SUBJECTS + ';';
The SUBJECT_LIST variable is already used in the preceding select. A silly mistake, but I am old.
Not that it matters since the Interbase UDF functions Locate() and Substr() can only handle 80 character strings, which makes them really useless to me... and probably useless to most.