SQL stands for Structured Query Language, which is a computer language used to store, manipulate, and retrieve data from a relational database. SQL is a database management language that supports database creation, deletion, obtaining rows, and altering rows, among other features.

In this tutorial, we will be learning about one such feature of SQL i.e rownum, and how it is used in SQL.

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SQL ROW_NUMBER Function

ROW_NUMBER function is a SQL ranking function that assigns a sequential rank number to each new record in a partition.

When the SQL Server ROW NUMBER function detects two identical values in the same partition, it assigns different rank numbers to both.

The rank number will be determined by the sequence in which they are displayed.

What are the Arguments in SQL?

SQL statements are composed of arguments, which are pieces of code that can be used to perform specific tasks. These arguments include SELECT, which is used to retrieve data from a database; INSERT, to add new records; UPDATE, to modify existing records; and DELETE, to delete specific records. Other arguments, such as WHERE and ORDER BY, are also used to refine the query and return specific results. With the right combination of statements, users can create complex queries that return precise data, allowing them to make informed decisions quickly.

Also Read: Top 35 SQL Server Interview Questions And Answers

SQL ROW_NUMBER Syntax

The syntax for ROW_NUMBER function in SQL is as follows-

ROW_NUMBER() OVER (
[PARTITION BY partition_expression, ... ]
ORDER BY sort_expression [ASC | DESC], ...
)

Now, let us look at the different clauses used in the syntax above.

OVER

This clause specifies the window or set of rows that the window function operates. The PARTITION BY and ORDER BY are the two possible clauses of the OVER clause.

PARTITION BY

It is an optional clause in the ROW_NUMBER function. It is a clause that divides the result set into partitions (groups of rows). The ROW_NUMBER() method is then applied to each partition, which assigns a separate rank number to each partition.

If the partition by clause is not specified, the ROW NUMBER function will treat the entire result as a single partition and rank it from top to bottom.

ORDER BY

Within each partition, this clause allows us to order the rows in the result set. Because the ROW NUMBER() function is order-dependent, it is a necessary clause.

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How to Use ROW_NUMBER in SQL Query?

Now that we have covered the basic syntax for writing the ROW_NUMBER function in SQL, let us look at an example to understand how it works with a SQL server table.

Example

For understanding how the ROW_NUMBER function works, we will use the Employee table as given below.

rownum_in_SQL_1

The given statement uses the ROW_NUMBER() to assign a sequential number to each employee in the table above.

SELECT

ROW_NUMBER() OVER (

ORDER BY E_id

) row_num,

E_name

FROM

Employee;

Output

rownum_in_SQL_2

Also Read: SQL Create Table: Basics of the Best Database Language

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What are Return Types in SQL?

SQL return types are an essential part of working with databases. This structure determines which data type is returned after executing an SQL statement. There are several different return types, including a single value, multiple values, an array of objects, and a table. Each return type will affect how the data is stored and accessed.

Functions, Stored Procedures, and Triggers can all return values in SQL. Those values can be of various data types, such as integer, string, date, or even a record or a table. Functions and Stored Procedures can use return statements to return any scalar data type or a table, and triggers can only produce a scalar value.

SQL_ROW_NUMBER_1

Using SQL ROW_NUMBER() for Pagination

The SQL ROW_NUMBER() function can be used to limit the number of returned rows for pagination purposes. This can benefit applications with large datasets, ensuring that users only receive the data they need. For example, an application may limit the number of rows returned to 20 at a time. The ROW_NUMBER() function is a valuable tool for paginating data sets and will enable applications to deliver faster results. The Row_Number() function can provide a unique sequential number for each row within the result set for a given SQL query. This sequential number can then be used to identify and access the data within a particular range of pages. Additionally, the Row_Number() function can be combined with the ORDER BY clause to ensure that the same order is maintained when the data is paginated.

SQL_ROW_NUMBER_2

Using SQL ROW_NUMBER() for Finding the nth Highest Value Per Group

Using the ROW_NUMBER() function, we can find the nth highest value per group. This can be done by specifying a condition in the ‘PARTITION BY’ clause that divides the data into groups and then ordering the data within each group by the value of interest. The ROW_NUMBER() function can then identify the row with the nth highest value within each group. This powerful feature allows us to identify and analyze data within each group quickly. This can be done by assigning the ROW_NUMBER() function to each row of data and then using the Partition clause to group the data by a specific value. The Nth highest value can then be determined by using the ORDER BY clause to sort the data in descending order and determine the value of the Nth row. This powerful technique for managing data sets of any size will allow applications to access and return the desired data quickly.

SQL_ROW_NUMBER_3

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Creating a Table in SQL Server

Creating tables in SQL Server is an essential skill for any developer, and it allows you to define the structure of your database and the relationships between objects. When creating a table, you need to consider the data types and sizes that best fit the application’s needs. Additionally, it would be best to consider constraints such as primary and foreign keys.

The first step is to open the SQL Server Management Studio (SSMS) and connect to an instance of the database engine. Next, right-click on the database name in the Object Explorer window and select New Table. This will open a new query window with a template for creating a table.

SQL_ROW_NUMBER_4

ROW_NUMBER with Other Ranking Functions in SQL

ROW_NUMBER is a function in the database language Transact-SQL that assigns a unique sequential number to each row in the result set of a query. It is typically used in conjunction with other ranking functions such as DENSE_RANK, RANK, and NTILE to perform various types of ranking analysis. ROW_NUMBER is also used in reporting applications to display a sequential number for each row in the report. This can help sort by criteria that don’t appear in the information or for debugging complex statements.

This paper aims to analyze the usage of ROW_NUMBER along with other ranking functions in SQL databases. Our goal is to explore the various options available and to understand their advantages and disadvantages in the context of data retrieval. We will also explore how different ranking functions can be combined to create a comprehensive solution for data retrieval. To do this, we will provide examples of how ROW_NUMBER and other ranking functions can be used and discuss their respective strengths and weaknesses.

SQL_ROW_NUMBER_5.

How to Use the SQL ROW_NUMBER Function With PARTITION BY ?

The following statement uses the ROW_NUMBER function to sequentially assign an integer to each employee in the table. The partition clause has been used here to divide the different employees based on their country.

SELECT

   E_name,

   E_country,

   ROW_NUMBER() OVER (

   PARTITION BY E_country

   ORDER BY E_name

   ) row_num

FROM

   Employee

ORDER BY

   E_country;

Output

rownum_in_SQL_3

As you can see in the output above that each employee has been divided based on the country. The sequentially assigned integer, or ROW_NUMBER reinitializes every time the name of the country is changed.

How to Use SQL ROW_NUMBER() Function without PARTITION BY?

The SQL ROW_NUMBER() function is often used to assign a unique row number to each record in your result set. When you use the ROW_NUMBER() function without the PARTITION BY clause, it treats the entire result set as a single partition, numbering the rows sequentially across the entire set, rather than restarting the count for each new partition. This could be particularly useful when you need a unique identifier for each row irrespective of any categorization. The function does need an ORDER BY clause, however, to determine the sequence of the numbering.

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How to Return a Subset of Rows Using CTE and ROW_NUMBER?

In applications, the ROW NUMBER() method is used for pagination. You can, for example, present a list of customers by page, with 10 rows each page.

The given code statement shows the use of ROW_NUMBER function to return employee rows from 1 to 5.

CTE is defined as "common table expression." A CTE allows you to create a named temporary result set that is available in the execution scope of SELECT, INSERT, UPDATE, DELETE, or MERGE statements.

WITH cte AS (

SELECT

     ROW_NUMBER() OVER(

          ORDER BY

             E_name

     ) row_num,

     E_id,

     E_name

  FROM

     Employee

) SELECT

E_id,

E_name

FROM

cte

WHERE

row_num > 1 AND

row_num <= 5;

Output

rownum_in_SQL_4.

In the example above, CTE uses the ROW NUMBER() method to assign a sequential integer to each row in the result set.

Second, the outer query returned the rows with row numbers ranging from 1to 5.

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Conclusion

In this article we learned about the ROW_NUMBER function in SQL and how is it used in different situations with partition and cte to obtain results according to our need. If you wish to learn more about SQL and get certified, checkout Simplilearn's SQL Certification Course

FAQs

1) How do I get row numbers in SQL?

To get row numbers in SQL, you can use the ROW_NUMBER() function. It assigns a unique sequential number to each row in the result set, based on the specified ordering.

2) What is row ID and row number in SQL?

In SQL, the row ID refers to a unique identifier assigned to each row in a table by the database management system. It is often an internal mechanism used by the database to track and locate rows efficiently. On the other hand, the row number is a sequential number assigned to each row in the result set based on a specified order, typically using the ROW_NUMBER() function.

3) How to group by row number in SQL?

To group by row number in SQL, you can use a subquery or a common table expression (CTE). First, assign row numbers to each row using the ROW_NUMBER() function. Then, in the outer query, group the rows by their assigned row numbers.

4) What is ROW_NUMBER () over partition by?

ROW_NUMBER() OVER PARTITION BY is a SQL function that assigns a unique sequential number to each row within a specific partition. A partition is a subset of rows that share the same values in the specified columns. The ROW_NUMBER() function resets the numbering for each partition, resulting in unique row numbers within each partition.

5) What is Rownum 1 in SQL?

Rownum 1 in SQL is not a standard SQL syntax. However, in some database systems like Oracle, Rownum is a pseudocolumn that can be used to limit the number of rows returned in a query. Rownum 1 is often used to retrieve only the first row from a result set. For example, "SELECT * FROM table WHERE ROWNUM = 1" would return the first row of the table.

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