A scheme of DWS migrating Oracle's CONNECT BY syntax

Abstract: This article provides a GaussDB DWS migration CONNECT BY syntax solution.

This article is shared from Huawei Cloud Community " GaussDB (DWS) Migration - Oracle Compatibility - CONNECT BY Migration ", author: a file in the back.

CONNECT BY NOCYCLE

1) Preset object definition

DROP SCHEMA IF EXISTS "sdifin" CASCADE;
CREATE SCHEMA "sdifin";
DROP TABLE IF EXISTS "sdifin"."ogg_ets_bas_instrument_t_2670";
SET search_path = sdifin;
CREATE TABLE ogg_ets_bas_instrument_t_2670 (
 bas_instrument_id numeric NOT NULL,
 instrument_name character varying(600),
 instrument_parent_id numeric,
 status numeric
)
WITH (enable_hstore=on, orientation=column, compression=yes, enable_delta=false, colversion=2.0, max_batchrow=60000)
DISTRIBUTE BY HASH(bas_instrument_id);
DROP TABLE IF EXISTS "sdifin"."ogg_sectype_2360";
SET search_path = sdifin;
CREATE TABLE ogg_sectype_2360 (
 thekey character varying(18) NOT NULL,
        name character varying(150)
)
WITH (enable_hstore=on, orientation=column, compression=yes, enable_delta=false, colversion=2.0, max_batchrow=60000)
DISTRIBUTE BY REPLICATION;

2) oracle original statement

SELECT
 to_char(i.BAS_INSTRUMENT_ID) AS INSTRUMENT_ID,
 to_char(i.INSTRUMENT_PARENT_ID) AS parent_thekey,
    TRIM(i.INSTRUMENT_NAME) AS INSTRUMENT_NAME,
    SYS_CONNECT_BY_PATH(i.INSTRUMENT_NAME, ';') AS INSTRUMENT_PATH,
    SYS_CONNECT_BY_PATH(i.BAS_INSTRUMENT_ID, '->') AS BAS_ID_PATH,  
 LEVEL AS INSTRUMENT_LEVEL,
    CONNECT_BY_ISCYCLE AS CYCLE_ERROR,
 2670 AS ss_id
 FROM OGG_ETS_BAS_INSTRUMENT_T_2670 i, OGG_SECTYPE_2360 s2
WHERE upper(i.instrument_name) = upper(TRIM(s2.name(+)))
AND s2.thekey IS NULL AND I.STATUS = 1
CONNECT BY NOCYCLE PRIOR i.BAS_INSTRUMENT_ID = i.INSTRUMENT_PARENT_ID
START WITH i.instrument_parent_id IS NULL

Execution plan in oracle

key point:

1) Statement features: the WHERE clause in the SQL statement contains non-associated conditions

2) Execution features: the non-associated condition calculation priority in the WHERE clause is lower than that of CONNECT BY, that is, these conditions will be filtered after CONNECT BY is executed, such as the above FILTER condition with id=2

3) DWS equivalent rewriting logic

WITH RECURSIVE TMP_ETC AS (
 SELECT
 to_char(i.bas_instrument_id) AS instrument_id,
 to_char(i.instrument_parent_id) AS parent_thekey,
        trim(i.instrument_name) AS instrument_name,
 ';'||i.instrument_name AS instrument_path,
 '->'||i.bas_instrument_id AS bas_id_path,
 1 AS instrument_level,
 0 AS cycle_error,
 2670 AS ss_id,
        s2.thekey,
 i.status,
 i.bas_instrument_id AS start_val
 FROM sdifin.ogg_ets_bas_instrument_t_2670 i
 LEFT JOIN sdifin.ogg_sectype_2360 s2 ON upper(trim(i.instrument_name)) = upper(trim(s2.name))
 WHERE i.instrument_parent_id IS NULL
 UNION ALL
 SELECT
 to_char(i.bas_instrument_id) AS instrument_id,
 to_char(i.instrument_parent_id) AS parent_thekey,
        trim(i.instrument_name) AS instrument_name,
        (b.instrument_path ||';'||i.instrument_name) AS instrument_path,
        (b.bas_id_path ||'->'||i.bas_instrument_id) AS bas_id_path,
 b.instrument_level+1 AS instrument_level,
        decode(trim(i.bas_instrument_id)=b.start_val,false,0,1) AS cycle_error,
 2670 AS ss_id,
        s2.thekey,
 i.status,
 b.start_val AS start_val
 FROM sdifin.ogg_ets_bas_instrument_t_2670 i
 LEFT JOIN sdifin.ogg_sectype_2360 s2 ON upper(i.instrument_name) = upper(trim(s2.name))
 INNER JOIN tmp_etc b ON b.instrument_id = i.instrument_parent_id
 WHERE b.cycle_error <> 1
)
SELECT 
 instrument_id,
 parent_thekey,
 instrument_name,
 instrument_path,
 bas_id_path,
 instrument_level,
 cycle_error,
 ss_id
FROM tmp_etc
WHERE thekey IS NULL
AND status = 1

 

Click to follow and learn about Huawei Cloud's fresh technologies for the first time~

{{o.name}}

{{m.name}}