This function computes the result of expr on the row that is precisely offset rows prior to the current row in the partition.



Usage Notes

  • LAG is only available as an analytic function (i.e., in combination with an over_clause). For more information, refer to Analytic Functions section.
  • The over_clause has to contain an order_clause and must not contain a window_frame_clause.
  • If the order_clause does not define an unique sort order, the result is non-deterministic.
  • The offset parameter has to be a numeric value greater than or equal to 0. Without offset, Exasol uses the default value 1.
  • If there are less than offset number of rows before the current row in the partition, LAG returns the default value for the row. Without specified default, Exasol uses NULL.
  • If the function contains IGNORE NULLS, Exasol skips rows with NULL during the search for the leading row in the partition. It does not skip any rows with RESPECT NULLS. If the function contains neither IGNORE NULLS nor RESPECT NULLS the default is RESPECT NULLS. The use of IGNORE NULLS is computationally more expensive than RESPECT NULLS.
  • To access following rows you can use the function LEAD.


Analytic Functions

    id, department, hire_date, 
    LAG(id, 1) OVER (PARTITION BY department ORDER BY hire_date) LAG 
FROM employee_table ORDER BY department, hire_date;
2005 ACCOUNTS 2013-01-01 NULL
2003 ACCOUNTS 2015-07-01 2005
2002 ACCOUNTS 2017-01-0 2003
2004 ACCOUNTS 2017-01-0 2002
2001 ACCOUNTS 2018-07-01 2004
1003 HR 2014-01-01 NULL
1002 HR 2016-01-01 1003
1004 HR 2016-01-01 1002
1001 HR 2018-01-01 1004