[SOLVED] LAG is not a recognized built in function name

LAG is not a recognized built in function name

I have a script that creates the following stored procedure :

CREATE PROCEDURE [dbo].[GetDurationFree] 
    @EquipmentName varchar(50)
AS
    UPDATE dbo.EquipmentMessages
    SET UnlockDuration = (SELECT DATEDIFF (SECOND, 
                (SELECT TOP 1 LAG(TimeUnlock) OVER (ORDER BY TimeUnlock) TimeUnlock
                    FROM dbo.EquipmentMessages
                    WHERE EquipmentName = @EquipmentName
                    ORDER BY TimeLock DESC), 
                (SELECT TOP 1 TimeLock FROM dbo.EquipmentMessages
                    WHERE EquipmentName = @EquipmentName
                    ORDER BY TimeLock DESC)))
    WHERE TimeLock = (SELECT MAX(TimeLock) FROM dbo.EquipmentMessages
                    WHERE EquipmentName = @EquipmentName);

The only problem is that It uses a Lag, when I try to execute it I get the following errors :

Msg 195, Level 15, State 10, Procedure GetDurationFree, Line 6
'LAG' is not a recognized built-in function name.

Msg 156, Level 15, State 1, Procedure GetDurationFree, Line 12
Incorrect syntax near the keyword 'ORDER'.

I was reading online and someone suggested the following :

ALTER DATABASE yourDBName
SET COMPATIBILITY_LEVEL = 110

However when I run this, I get the following error :

Msg 15048, Level 16, State 1, Line 1
Valid values of the database compatibility level are 80, 90, or 100.

I am running

SQL Server 2014 Management Studio, the express version

However when I enter the following SELECT @@version

I get :

Microsoft SQL Server 2008 (SP1) - 10.0.2531.0 (X64) 
Mar 29 2009 10:11:52 
Copyright (c) 1988-2008 Microsoft Corporation
Express Edition (64-bit) on Windows NT 6.1 <X64> (Build 7601: Service Pack 1)

Solution

What I ended up doing is going into the control panel under uninstall a program and deleted everything that has to do with SQL. Then I re installed the program and It worked fine.

I noticed that there a early version of 2008 on the computer that wasn't installed. Maybe the problem comes from there.