Q:

IF NULL SQL returning error

I want a SQL query to return "VIDE" when the field is empty in Sales Cloud but I have an error message saying "Incorrect syntax near the keyword 'IF'. 
Here is my SQL part : 
IF NULL (Code_Provenance__c, 'VIDE') as 'CODE_PROVENANCE',

A:

There are a few ways to resolve this (I know you mentioned in your comments that you utilized CASE to solve for it, but thought i should leave something as a reference for anyone else having this issue):

CASE statements:

SELECT primarykey,
CASE
  WHEN field1 IS NULL THEN
    'Default Value'
  ELSE 
    field1
END as field1
FROM [myDE]

ISNULL

SELECT primarykey,
ISNULL(field1,'Default Value') as field1
FROM [myDE]

COALESCE

SELECT primarykey,
COALESCE(field1,'Default Value') as field1
FROM [myDE]

There may be a couple other ways to accomplish this, but these are three should handle most if not all use cases you may have.