What is the use of WITH TIES keyword in SELECT statement in SQL Queries?

Understanding the 'WITH TIES' Keyword in SQL SELECT Statements

Explore the functionality of the WITH TIES clause in SQL Server's SELECT statements, how it works with TOP, and practical examples for retrieving additional rows.

When working with SQL queries, especially when you need to limit the number of results, the TOP clause is incredibly useful. However, what happens if the 'top N' results include rows that share the same value in the ORDER BY column as the Nth row? This is where the WITH TIES keyword comes into play, providing a powerful way to ensure you don't inadvertently exclude relevant data.

What is 'WITH TIES'?

The WITH TIES keyword is an optional clause that can be used in conjunction with the TOP clause in a SELECT statement. Its primary purpose is to include all rows that tie for the last place in the limited result set, based on the ORDER BY clause. Without WITH TIES, TOP N would simply return the first N rows, even if the Nth row has identical sorting values to subsequent rows that would otherwise be excluded.

How 'WITH TIES' Works

When you specify TOP N WITH TIES, SQL Server first sorts the entire result set according to the ORDER BY clause. It then identifies the Nth row. After that, it includes all rows from the sorted set up to and including any rows that have the exact same values in the ORDER BY columns as the Nth row. This means the final result set might contain more than N rows.

flowchart TD
    A[Start SELECT Query] --> B{Has TOP N clause?}
    B -- No --> C[Return all results]
    B -- Yes --> D{Has ORDER BY clause?}
    D -- No --> E[Error: WITH TIES requires ORDER BY]
    D -- Yes --> F[Sort results by ORDER BY]
    F --> G[Identify Nth row]
    G --> H{Has WITH TIES?}
    H -- No --> I[Return first N rows]
    H -- Yes --> J[Include Nth row and all tied rows]
    J --> K[Return final result set]
    K --> L[End]

Flowchart illustrating the logic of TOP N and TOP N WITH TIES.

Practical Examples

Let's consider a scenario with a simple Products table to demonstrate the difference between TOP N and TOP N WITH TIES.

CREATE TABLE Products (
    ProductID INT PRIMARY KEY,
    ProductName VARCHAR(50),
    Price DECIMAL(10, 2)
);

INSERT INTO Products (ProductID, ProductName, Price) VALUES
(1, 'Laptop', 1200.00),
(2, 'Mouse', 25.00),
(3, 'Keyboard', 75.00),
(4, 'Monitor', 300.00),
(5, 'Webcam', 75.00),
(6, 'Headphones', 150.00),
(7, 'Speaker', 75.00),
(8, 'Printer', 200.00);

SQL script to create and populate a sample Products table.

Example 1: Using TOP N without WITH TIES

Suppose we want to find the top 3 cheapest products. Without WITH TIES, if there are multiple products with the same price as the 3rd cheapest, only the first ones encountered (based on internal ordering or secondary sort if specified) will be returned.

SELECT TOP 3 ProductID, ProductName, Price
FROM Products
ORDER BY Price ASC;

Query to get the top 3 cheapest products without WITH TIES.

Expected Output (may vary slightly depending on internal order for ties):

ProductID | ProductName | Price
----------|-------------|-------
2         | Mouse       | 25.00
3         | Keyboard    | 75.00
5         | Webcam      | 75.00

Notice that 'Speaker' (ProductID 7) also has a price of 75.00, but it's excluded because TOP 3 strictly limits the count to three rows.

Example 2: Using TOP N WITH TIES

Now, let's use WITH TIES to include all products that share the same price as the 3rd cheapest product.

SELECT TOP 3 WITH TIES ProductID, ProductName, Price
FROM Products
ORDER BY Price ASC;

Query to get the top 3 cheapest products including ties.

Expected Output:

ProductID | ProductName | Price
----------|-------------|-------
2         | Mouse       | 25.00
3         | Keyboard    | 75.00
5         | Webcam      | 75.00
7         | Speaker     | 75.00

In this case, 'Speaker' (ProductID 7) is included because its price (75.00) ties with the price of 'Keyboard' (ProductID 3) and 'Webcam' (ProductID 5), which are part of the top 3 cheapest. The result set now contains 4 rows instead of 3.

Limitations and Considerations

While WITH TIES is powerful, it's important to be aware of its implications:

• Performance: Including WITH TIES might slightly impact performance if there are many ties, as the database engine needs to evaluate more rows to determine the full set of ties.
• Result Set Size: The number of rows returned can be greater than the specified N. Your application logic should be prepared to handle a variable number of rows.
• ORDER BY Requirement: As mentioned, ORDER BY is mandatory. If your query doesn't inherently need an order, you might need to add one (e.g., by a primary key) to use WITH TIES effectively.
• Compatibility: WITH TIES is a feature primarily found in SQL Server. Other database systems might have different syntax or approaches for similar functionality (e.g., using window functions like RANK() or DENSE_RANK()).

In conclusion, WITH TIES is a valuable tool in SQL Server for scenarios where you need to retrieve a limited number of rows but also want to include all rows that share the same sorting criteria as the last row in that limit. It ensures that no relevant data is arbitrarily excluded due to ties in the ORDER BY clause.