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How use LAG Oracle analytic function

Oracle 11g introduces the LAG() function, a powerful analytic tool that allows you to access data from previous rows without needing a self-join. The LAG() function retrieves data from a specific offset before the current row, making it ideal for tasks like comparing consecutive entries.

Very usefully new features in Oracle 11g is analytic Oracle SQL function LAG.

Oracle LAG() is an analytic function that allows you to access the row at a given offset before the current row without using a self-join.

The following illustrates the syntax of the LAG() function:

LAG(expression [, offset ] [, default ]) OVER ( [ query_partition_clause ] order_by_clause )

SQL query LAG

This code find change in address post code in journal table:

  SELECT  *
    FROM  (
              SELECT  t1.SITE_NUMBER
                     ,t1.JN_DATETIME
                     ,t1.ADR_POSTCODE
                     ,LAG (t1.ADR_POSTCODE, 1) OVER (PARTITION BY t1.SITE_NUMBER ORDER BY t1.jn_datetime) AS PREV_ADR_POSTCODE
                FROM  t1 
          )
   WHERE      adr_postcode = '00-001'
          AND PREV_ADR_POSTCODE <> '00-001'
          AND PREV_ADR_POSTCODE <> '00-000'
ORDER BY  SITE_NUMBER;

Test query data

CREATE TABLE T1
(
  SITE_NUMBER   VARCHAR2(16 BYTE),
  JN_DATETIME   DATE,
  ADR_POSTCODE  VARCHAR2(20 BYTE)
)
LOGGING 
NOCOMPRESS 
MONITORING;" message="" highlight="" provider="manual"/][pastacode lang="sql" manual="SET DEFINE OFF;
Insert into KPREISKORN.T1
   (SITE_NUMBER, JN_DATETIME, ADR_POSTCODE)
 Values
   ('20001', TO_DATE('08/01/2017 15:01:31', 'MM/DD/YYYY HH24:MI:SS'), '00-001');
Insert into KPREISKORN.T1
   (SITE_NUMBER, JN_DATETIME, ADR_POSTCODE)
 Values
   ('20002', TO_DATE('04/20/2017 11:59:29', 'MM/DD/YYYY HH24:MI:SS'), '00-002');
Insert into KPREISKORN.T1
   (SITE_NUMBER, JN_DATETIME, ADR_POSTCODE)
 Values
   ('20001', TO_DATE('06/15/2017 04:02:41', 'MM/DD/YYYY HH24:MI:SS'), '00-003');
Insert into KPREISKORN.T1
   (SITE_NUMBER, JN_DATETIME, ADR_POSTCODE)
 Values
   ('20004', TO_DATE('06/20/2017 20:15:13', 'MM/DD/YYYY HH24:MI:SS'), '00-001');
Insert into KPREISKORN.T1
   (SITE_NUMBER, JN_DATETIME, ADR_POSTCODE)
 Values
   ('20001', TO_DATE('12/10/1929 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), '00-001');
Insert into KPREISKORN.T1
   (SITE_NUMBER, JN_DATETIME, ADR_POSTCODE)
 Values
   ('20001', TO_DATE('09/25/2091 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), '00-003');
Insert into KPREISKORN.T1
   (SITE_NUMBER, JN_DATETIME, ADR_POSTCODE)
 Values
   ('20001', TO_DATE('09/14/1914 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), '00-001');
Insert into KPREISKORN.T1
   (SITE_NUMBER, JN_DATETIME, ADR_POSTCODE)
 Values
   ('20001', TO_DATE('03/25/1911 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), '00-001');
Insert into KPREISKORN.T1
   (SITE_NUMBER, JN_DATETIME, ADR_POSTCODE)
 Values
   ('20001', TO_DATE('11/22/2029 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), '00-001');
COMMIT;