OracleDBAの技術メモ

SELECT COUNT(*) FROM (
SELECT DISTINCT TEST_TYPE FROM TEST_TABLE);

SELECT COUNT(DISTINCT TEST_TYPE) FROM TEST_TABLE;

begin
    DBMS_STATS.GATHER_TABLE_STATS(
        ownname => '&owner'
    ,   tabname => '&table'
    ,   method_opt => 'FOR ALL COLUMNS SKEWONLY'
    );
end;
/

SELECT
    tst.id
,   tst.seqno
FROM t_test tst
WHERE tst.seqno = (
--
SELECT
    MAX(tstx.seqno)
FROM t_test tstx
WHERE tstx.id = tst.id
--
);

SELECT
    tst.id
,   tst.seqno
FROM t_test tst
    INNER JOIN t_test tstx
        ON  tstx.id = tst.id
GROUP BY
    tst.id
,   tst.seqno
HAVING tst.seqno = max(tstx.seqno)
;

～
(
SELECT
    tst.id
,   tst.seqno
FROM t_test tst
    INNER JOIN t_test tstx
        ON  tstx.id = tst.id
WHERE tst.id = [親クエリーのテーブル].id
  AND tstx.id = [親クエリーのテーブル].id
GROUP BY
    tst.id
,   tst.seqno
HAVING tst.seqno = max(tstx.seqno)
)
～