SQL Server

Introduction

The behavior of Mendix using a Microsoft SQL Server database has some minor differences when compared with using a PostgreSQL database. These differences are documented below.

See also Microsoft SQL Server for information about setting up a SQL Server database to use with Mendix.

Behavior of Uniqueness Constraint with Nulls

When an attribute has a validation rule of Type Unique, the Mendix runtime creates a uniqueness constraint in the database for the corresponding database column.

If two different objects have a value of null for that attribute, SQL Server will treat them as equal and raise a unique constraint violation, causing an error.

Other databases treat all occurrences of null as unequal to each other, allowing multiple objects with a null value for the attribute.