# Comparing Database Objects
## Introduction
Database object can either be compared in SQL `WHERE` clauses or in programming code.
## Comparison in SQL Queries
In SQL queries database objects can be compared either by the equals `=` operator or by the `ObjectNo` value. The direct comparison is always preferable.
```csharp
var products = Db.SQL(
"SELECT p FROM Product p WHERE p.Customer = ?", customer);
```
```csharp
var products = Db.SQL(
"SELECT p FROM Product p WHERE p.Customer.ObjectNo = ?",
customer.GetObjectNo());
```
## Comparison Between Instances
Two instances of a database class can be compared either with the `Object.Equals` method or with the `ObjectNo` value. The `Object.Equals` method is the preferable way.
```csharp
var firstProduct = new Product();
var secondProduct = new Product();
var anotherFirstProduct = Db.FromId(firstProduct.GetObjectNo());
firstProduct.Equals(secondProduct); // false
firstProduct.GetObjectNo() == secondProduct.GetObjectNo(); // false
firstProduct.Equals(anotherFirstProduct); // true
firstProduct.GetObjectNo() == anotherFirstProduct.GetObjectNo(); // true
```
{% hint style="warning" %}
The equals `==` operator and the `Object.ReferenceEquals` method will always return `false` when comparing database objects.
{% endhint %}
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