How to Transform a One-to-Many Relationship into Separate Columns in Informix SQL?

How to Display a One-to-Many Relationship as Separate Columns

Problem:

To transform data from a format like:

id     codes

63592  PELL
58640  SUBL
58640  USBL
73571  PELL
73571  USBL
73571  SUBL

into:

id     codes 

63592  PELL
58640  SUBL, USBL
73571  PELL, USBL, SUBL

Solution:

Utilizing a user-defined aggregate in Informix SQL can achieve this transformation.

CREATE FUNCTION gc_init(dummy VARCHAR(255)) RETURNING LVARCHAR;
    RETURN '';
END FUNCTION;

CREATE FUNCTION gc_iter(result LVARCHAR, value VARCHAR(255))
    RETURNING LVARCHAR;
    IF result = '' THEN
        RETURN TRIM(value);
    ELSE
        RETURN result || ',' || TRIM(value);
    END IF;
END FUNCTION;

CREATE FUNCTION gc_comb(partial1 LVARCHAR, partial2 LVARCHAR)
    RETURNING LVARCHAR;
    IF partial1 IS NULL OR partial1 = '' THEN
        RETURN partial2;
    ELIF partial2 IS NULL OR partial2 = '' THEN
        RETURN partial1;
    ELSE
        RETURN partial1 || ',' || partial2;
    END IF;
END FUNCTION;

CREATE FUNCTION gc_fini(final LVARCHAR) RETURNING LVARCHAR;
    RETURN final;
END FUNCTION;

CREATE AGGREGATE group_concat
    WITH (INIT = gc_init, ITER = gc_iter,
          COMBINE = gc_comb, FINAL = gc_fini);

Example:

Applying this aggregate to the sample data with the following query:

SELECT id, group_concat(codes)
    FROM anonymous_table
    GROUP BY id;

Will produce the desired output:

58640 SUBL,USBL
63592 PELL
73571 PELL,SUBL,USBL
73572 PELL,SUBL,USBL

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