If you’re getting error message 4112 that reads “The function ‘LAG’ must have an OVER clause with ORDER BY” in SQL Server, it’s probably because you’re omitting the ORDER BY clause from the OVER clause when using the LAG() function.

The LAG() function requires an OVER clause that contains an ORDER BY clause. This error happens when we include the OVER clause but not the ORDER BY clause.

To fix this error, add an ORDER BY clause to the OVER clause.

Example of Error

Here’s an example of code that results in the error:

SELECT
    VendorId,
    ProductName,
    ProductPrice,
    LAG( ProductPrice ) OVER ( ) AS LAG
FROM Products;

Result:

Msg 4112, Level 15, State 1, Line 5
The function 'LAG' must have an OVER clause with ORDER BY.

The error occurred because, although I provided an OVER clause, it doesn’t contain an ORDER BY clause.

Note that simply adding an ORDER BY clause to the end of the query does not fix the issue:

SELECT
    VendorId,
    ProductName,
    ProductPrice,
    LAG( ProductPrice ) OVER ( ) AS LAG
FROM Products
ORDER BY ProductPrice;

Result:

Msg 4112, Level 15, State 1, Line 5
The function 'LAG' must have an OVER clause with ORDER BY.

While it’s fine to have an ORDER BY clause at the end of the query, there still needs to be one in the OVER clause.

Solution

To fix this issue, all we need to do is add an ORDER BY clause to the OVER clause:

SELECT
    VendorId,
    ProductName,
    ProductPrice,
    LAG( ProductPrice ) OVER ( 
        ORDER BY ProductPrice 
        ) AS LAG
FROM Products;

Result:

VendorId  ProductName                      ProductPrice  LAG  
--------  -------------------------------  ------------  -----
1004      Bottomless Coffee Mugs (4 Pack)  9.99          null 
1003      Hammock                          10            9.99 
1001      Long Weight (green)              11.99         10   
1004      Tea Pot                          12.45         11.99
1001      Long Weight (blue)               14.75         12.45
1001      Left handed screwdriver          25.99         14.75
1001      Right handed screwdriver         25.99         25.99
1002      Sledge Hammer                    33.49         25.99
1003      Straw Dog Box                    55.99         33.49
1003      Chainsaw                         245           55.99

This time the function worked as expected, without error.

The OVER clause can also have a PARTITION BY clause, but this is optional. We can omit the PARTITION BY clause, but not the ORDER BY clause.