Re: query decorrelation in postgres

I am sorry for not elaborating on that. What I meant by de-correlation was optimizing a query to get rid of sub-queirs by using joins.

eg. In the TPC-H schema, a query to find out the names of suppliers who supply parts having size  < 100

Query with nested subqueries:

SELECT 
    S_NAME
FROM
    SUPPLIER
WHERE
    S_SUPPKEY
    IN (
        SELECT
            PS_SUPPKEY
        FROM
            PARTSUPP
        WHERE
            PS_PARTKEY
                IN (
                    SELECT
                        P_PARTKEY
                    FROM
                        PART
                    WHERE
                        P_SIZE < 100
                )



Query with joins without subqueries:


SELECT
    S_NAME
FROM
    SUPPLIER
INNER JOIN
    PARTSUPP
ON
    S_SUPPKEY = PS_SUPPKEY
INNER JOIN
    PART
ON
    P_PARTKEY = PS_PARTKEY
WHERE
    P_SIZE < 100



Thanks,
Mahendra