oracleoracle12c

hierarchical table connect left element with right


I have a problem with creating Hierarchical table,

I have the following data

    With data(left_code, left_category, right_code, right_category) as (
    SELECT '21BEMVXP040150FIS4', 'A', '21CYMVXP040152VFO4', 'B' FROM DUAL UNION ALL
    SELECT '21CYMVXP040152VFO4', 'B', '23FRDDS2NCNF1LOBR4', 'C' FROM DUAL UNION ALL
    SELECT '22NLDDS2ACNF3MQJC4', 'B', '21BEMVXP040150FIS9', 'A' FROM DUAL UNION ALL
    SELECT '21BEMVXP040150FIS9', 'A', '23FRDDS2NCNF1LOBR9', 'C' FROM DUAL UNION ALL
    SELECT '21DEMVXP040222UJK5', 'B', '23FRDDS4NCNF1LOBR4', 'C' FROM DUAL UNION ALL
    )
    SELECT *
      FROM data;

I want to connect the left_code with right_code

The desired output should look like this:

CODE_1 CATEGORY_1 CODE_2 CATEGORY_2 CODE_3 CATEGORY_3
21BEMVXP040150FIS4 A 21CYMVXP040152VFO4 B 23FRDDS2NCNF1LOBR4 C
22NLDDS2ACNF3MQJC4 B 21BEMVXP040150FIS9 A 23FRDDS2NCNF1LOBR9 C
21DEMVXP040222UJK5 B 23FRDDS4NCNF1LOBR4 C NULL NULL
22NLDDS2ACNF3MQJC2 A 22FRDDS2NCNF1LOBR0 C NULL NULL

Could you help me please ?


Solution

  • You can use a hierarchical query (which will only query the table once):

    SELECT CONNECT_BY_ROOT left_code AS code_1,
           CONNECT_BY_ROOT left_category AS category_1,
           CONNECT_BY_ROOT right_code AS code_2,
           CONNECT_BY_ROOT right_category AS category_2,
           CASE LEVEL WHEN 2 THEN right_code END AS code_3,
           CASE LEVEL WHEN 2 THEN right_category END AS category_3
    FROM   data
    WHERE  LEVEL = 2
    OR     (LEVEL = 1 AND CONNECT_BY_ISLEAF = 1)
    CONNECT BY PRIOR right_code = left_code;
    

    or a LEFT OUTER JOIN to the same table (which will query the table twice):

    SELECT d1.left_code AS code_1,
           d1.left_category AS category_1,
           d1.right_code AS code_2,
           d1.right_category AS category_2,
           d2.right_code AS code_3,
           d2.right_category AS category_3
    FROM   data d1
           LEFT OUTER JOIN data d2
           ON d1.right_code = d2.left_code;
    

    Which, for the sample data:

    CREATE TABLE data( left_code, left_category, right_code, right_category ) as
      SELECT '21BEMVXP040150FIS4', 'A', '21CYMVXP040152VFO4', 'B' FROM DUAL UNION ALL
      SELECT '21CYMVXP040152VFO4', 'B', '23FRDDS2NCNF1LOBR4', 'C' FROM DUAL UNION ALL
      SELECT '22NLDDS2ACNF3MQJC4', 'B', '21BEMVXP040150FIS9', 'A' FROM DUAL UNION ALL
      SELECT '21BEMVXP040150FIS9', 'A', '23FRDDS2NCNF1LOBR9', 'C' FROM DUAL UNION ALL
      SELECT '21DEMVXP040222UJK5', 'B', '23FRDDS4NCNF1LOBR4', 'C' FROM DUAL;
    

    Both output:

    CODE_1 CATEGORY_1 CODE_2 CATEGORY_2 CODE_3 CATEGORY_3
    21BEMVXP040150FIS4 A 21CYMVXP040152VFO4 B 23FRDDS2NCNF1LOBR4 C
    21BEMVXP040150FIS9 A 23FRDDS2NCNF1LOBR9 C null null
    21CYMVXP040152VFO4 B 23FRDDS2NCNF1LOBR4 C null null
    21DEMVXP040222UJK5 B 23FRDDS4NCNF1LOBR4 C null null
    22NLDDS2ACNF3MQJC4 B 21BEMVXP040150FIS9 A 23FRDDS2NCNF1LOBR9 C

    fiddle