Using newline character and adding several rows of strings into one

Question

I have in my hands an old app on informix server and I'm migrating data into a different database. Both are informix databases. I have a particular problem with one table. Old app used it to support multiline text.

OldTable: HeaderID int LineNum int Descr nvarchar(50,1)

NewTable: HeaderID int Descr lvarchar(max)

So, for each HeaderID I have to read the descriptions ordered by line number and put them all together for insert into a new table. There has to be a newline character between each line for conversion to succeed.

Any tips on how to do this?

Answer 1

If you need to do it from SQL then you can use procedure:

CREATE FUNCTION get_text(aHeaderID int)
RETURNING lvarchar;
DEFINE result lvarchar;
DEFINE vcfld lvarchar;
    LET result=NULL;
    EXECUTE PROCEDURE IFX_ALLOW_NEWLINE('T');
    FOREACH cur1
        FOR SELECT Descr INTO vcfld FROM OldTable WHERE HeaderID = aHeaderID ORDER BY LineNum
        IF result IS NULL THEN
            LET result = vcfld;
        ELSE
            LET result = result || '
' || vcfld;
        END IF;
    END FOREACH;
    RETURN result;
END FUNCTION;

(notice usage of IFX_ALLOW_NEWLINE and line breaking when updating result)

Then you can fill NewTable using:

UPDATE NewTable SET Descr=get_text(HeaderID);

Answer 2

You can use PreparedStatement. This is example in Jython that uses JDBC Informix driver:

db = DriverManager.getConnection(db_url, usr, passwd)
pstm = db.prepareStatement("SELECT vc FROM src ORDER BY id")
rs = pstm.executeQuery()
lines = []
while (rs.next()):
    lines.append(rs.getString(1))
pstm = db.prepareStatement("INSERT INTO dest (lvc) VALUES (?)")
pstm.setString(1, '\n'.join(lines))
rs = pstm.execute()
db.close()