LAG

Description

Accesses data from a previous row in the same result set without the use of a self-join starting with SQL Server 2012 (11.x). LAG provides access to a row at a given physical offset that comes before the current row. Use this analytic function in a SELECT statement to compare values in the current row with values in a previous row. (COUNT in Transact-SQL).

Sample Source Pattern

Syntax

SQL Server

LAG (scalar_expression [,offset] [,default])  
    OVER ( [ partition_by_clause ] order_by_clause )  

Snowflake SQL

Snowflake SQL Documentation

COUNT( [ DISTINCT ] <expr1> [ , <expr2> ... ] )

Examples

SQL Server

Code:

SELECT TOP 10 
LAG(E.VacationHours,1) OVER(ORDER BY E.NationalIdNumber) as PREVIOUS,
E.VacationHours AS ACTUAL 
FROM HumanResources.Employee E

Result:

PREVIOUS|ACTUAL|
--------+------+
    NULL|    10|
      10|    89|
      89|    10|
      10|    48|
      48|     0|
       0|    95|
      95|    55|
      55|    67|
      67|    84|
      84|    85|

Snowflake SQL

Code:

SELECT TOP 10 LAG(E.VacationHours,1)
OVER(ORDER BY E.NationalIdNumber) as PREVIOUS,
E.VacationHours AS ACTUAL
FROM HumanResources.Employee E;

Result:

PREVIOUS|ACTUAL|
--------+------+
    NULL|    10|
      10|    89|
      89|    10|
      10|    48|
      48|     0|
       0|    95|
      95|    55|
      55|    67|
      67|    84|
      84|    85|