SQL provides a powerful set of tools like operators that allow you to perform various operations on your data. Set operators in SQL enable you to combine, compare, and analyze datasets.
In this article, we will explain all about set operators in SQL, their types, their functions, and practical applications.
Introduction to Set Operators in SQL
Set operators in SQL are a very powerful tool for manipulating and combining data from one or more tables. It helps to create complex queries and obtain valuable insights from the database. It helps to extract meaningful information from your database.
What are Set Operators in SQL?
Set Operators in SQL are used to combine, compare, or eliminate rows of data from multiple tables. The primary set operators are UNION, UNION ALL, INTERSECT, EXISTS, and EXCEPT, in SQL. Each of the set operators in SQL is used for unique purposes.
What is a Union Operator in SQL?
Union operator is being used to combine the result sets of two or more SELECT statements into a single result set. It eliminates duplicate rows, ensuring that the final result contains only distinct records.
It is useful when you need to consolidate data from multiple source tables. The number of fields and order should be the same in all the tables, and the data type must be compatible. You can put the same alias name for the columns in all the SELECT statements if not matching the field names exactly.
What is a Union All Operator in SQL?
Unlike UNION, the Union all operator is being used to combine the result sets of two or more SELECT statements into a single result set including duplicate records. You can put the same alias name for the columns of all the SELECT statements if not matching the field names exactly.
What is an Intersect Operator in SQL?
Intersect operator is being used to find common rows that exist in the result sets of two SELECT statements. It returns rows that are common between two or more result sets. This can be helpful when you want to identify overlapping data points within your database.
In other words, the intersect operator is used to combine two SELECT statements but returns rows only from the first SELECT statement that are identical to a row in the second SELECT statement. That means intersect returns only common rows returned by the two SELECT statements. You can put the same alias name for the columns of all the SELECT statements if not matching the field names exactly.
What is an Except Operator in SQL?
The except operator retrieves rows from the first SELECT statement that are not present in the result set of the second SELECT statement. It is useful for finding the difference between two sets of data. It is a great tool for pinpointing disparities in your data.
In other words, except operator is used to combine two SELECT statements and returns rows from the first SELECT statement that are not returned by the second SELECT statement. That means except returns only rows, which are not available in the second SELECT statement.
What is an Exists Operator in SQL?
The exists operator is being used in sub-queries to find records from the first SELECT statement that are present in the second SELECT statement in the sub-query. It is used to test the existence of any record in a sub-query and returns TRUE if the sub-query returns one or more records.
Difference between Union and Union All Operator
While the UNION operator eliminates duplicate rows, UNION ALL retains all rows from the involved SELECT statements, including duplicates.
Differences between Set Operators and Joins
Set Operators and Joins serve different purposes. While Joins combine rows from multiple tables based on related columns, Set Operators work with the result sets of SELECT statements, irrespective of the underlying tables.
Best Practices of Set Operators in SQL
When using Set Operators, it is essential to ensure that the SELECT statements involved compatible columns. Additionally, always consider the data types and data size to prevent unexpected results.
You can nest Set Operators to perform more complex operations. For example, you can use the Union Operator to merge two result sets and then use the Except Operator to find the differences in the merged set.
Disadvantages of Set Operators in SQL
While Set Operators are powerful, they can impact query performance, especially when dealing with large datasets. Ensure your database is appropriately indexed to optimize query execution.
Mis-using Set Operators can lead to incorrect results. Be cautious when using Union and Union All, as they can introduce unexpected duplicates into your final result.
Practical Scenarios of Set Operators in SQL
Set Operators can be used in various scenarios, such as data integration, data cleansing, and data analysis. Let’s explore some common use cases-
- Data Integration: When working with multiple data sources, you may need to combine data to create a unified dataset. Set Operators like UNION and UNION ALL are invaluable in this context. They allow you to merge data from different tables or databases, ensuring that you have a comprehensive view of your data.
- Data Cleansing: Data quality is crucial in database management. Set Operators, especially EXCEPT, help identify and eliminate duplicate or inconsistent data. By comparing tables and using EXCEPT, you can easily spot discrepancies and take corrective actions.
- Data Analysis: Set Operators are essential for data analysis tasks. For example, if you want to find common elements between two datasets, you can use the INTERSECT operator. This is particularly useful when working with customer data, product catalogs, or any scenario where you need to identify shared elements.
Applications of Set Operators in SQL
You will learn here all about the application of Set Operators in SQL as follows –
1. Application of UNION Operators in SQL
In this example, we have taken two different tables i.e. o_Course and o_Student where ID and Name are the columns in the o_Student table and Course_ID, Course_Name, and Student_ID are the columns in the o_Course table. As you can see the Student_ID is the common field between both the table. Now, we will try to combine and find the result sets of two SELECT statements into a single result set with distinct records using the UNION operator as follows –
As the column name of the first SELECT statement does not match the column names of the second SELECT statement, and hence we have provided alias names in the first statement columns –
Syntax:
SELECT Column1 AS [Column1],Column2 AS [Column2] FROM Table_Name_First
UNION
SELECT Column1,Column2 FROM Table_Name_Second
Example:
USE [SQLPOST]
SELECT ID AS [Student_ID],Name AS [Student_Name] FROM o_Student
UNION
SELECT Student_ID,Student_Name FROM o_Course
Screenshot: Below screenshot for reference –
Result: You can see in the above screenshot that the result set contains the distinct result and eliminated the duplicate records using the UNION operator.
2. Application of UNION ALL Operators in SQL
In this example, we have taken the same tables. Now, we will try to combine and find the result sets of two SELECT statements into a single result set with duplicate records using the UNION ALL operator as follows –
As the column name of the first SELECT statement does not match the column names of the second SELECT statement, and hence we have provided alias names in the first statement columns –
Syntax:
SELECT Column1 AS [Column1],Column2 AS [Column2] FROM Table_Name_First
UNION ALL
SELECT Column1,Column2 FROM Table_Name_Second
Example:
USE [SQLPOST]
SELECT ID AS [Student_ID],Name AS [Student_Name] FROM o_Student
UNION ALL
SELECT Student_ID,Student_Name FROM o_Course
Screenshot: Below screenshot for reference –
Result: You can see in the above screenshot that the result set contains the duplicate result using the UNION ALL operator.
3. Application of Intersect Operators in SQL
In this example, we have taken the same tables. Now, we will try to combine and find the result sets of two SELECT statements into a single result set with common records using the Intersect operator as follows –
As the column name of the first SELECT statement does not match the column names of the second SELECT statement, and hence we have provided alias names in the first statement columns –
Syntax:
SELECT Column1 AS [Column1],Column2 AS [Column2] FROM Table_Name_First
INTERSECT
SELECT Column1,Column2 FROM Table_Name_Second
Example:
USE [SQLPOST]
SELECT ID AS [Student_ID],Name AS [Student_Name] FROM o_Student
INTERSECT
SELECT Student_ID,Student_Name FROM o_Course
Screenshot: Below screenshot for reference –
Result: You can see in the above screenshot that the result set contains the common result using the INTERSECT operator.
4. Application of Except Operators in SQL
In this example, we will try to combine and find the result sets of two SELECT statements into a single result set which are not available in the second SELECT statement using the except operator as follows –
As the column name of the first SELECT statement does not match the column names of the second SELECT statement, and hence we have provided alias names in the first statement columns –
Syntax:
SELECT Column1 AS [Column1],Column2 AS [Column2] FROM Table_Name_First
EXCEPT
SELECT Column1,Column2 FROM Table_Name_Second
Example:
USE [SQLPOST]
SELECT ID AS [Student_ID],Name AS [Student_Name] FROM o_Student
EXCEPT
SELECT Student_ID,Student_Name FROM o_Course
Screenshot: Below screenshot for reference –
Result: You can see in the above screenshot that the result set contains the results that are not available in the second SELECT statement using the INTERSECT operator.
5. Application of Exists Operators in SQL
In this example, we will try to combine and find the result sets of two SELECT statements into a single result set which are available in the second SELECT statement using the exists operator as follows –
Syntax:
SELECT * FROM Table_Name_First WHERE EXISTS (SELECT Unique_Column_Name FROM Table_Name_First)
Example:
USE [SQLPOST]
SELECT * FROM o_Student WHERE EXISTS (SELECT Student_ID FROM o_Course)
Screenshot: Below screenshot for reference –
Result: You can see in the above screenshot that the result set contains the results that are available in the second SELECT statement using the EXISTS operator.
FAQs
Set operators in SQL allow you to combine, compare, and analyze datasets from one or more tables, enabling complex queries and data manipulation.
Set operators can identify data discrepancies and inconsistencies, helping to maintain data integrity during data cleaning.
While SQL databases excel in using set operators, their compatibility and limitations in NoSQL databases vary. Alternatives may be preferred in some cases.
UNION removes duplicate rows, while UNION ALL retains all rows from the involved SELECT statements, including duplicates.
You should use the UNION operator when you want to combine the result sets of multiple SELECT statements into a single result set, removing duplicates in the process.
It depends on the specific use case. Joins are suitable for combining data from related tables, while Set Operators are ideal for working with the result sets of SELECT statements.
Ensure that your database tables are properly indexed, and consider using WHERE clauses to filter data before applying Set Operators.
Yes, you can achieve similar results using subqueries or JOIN operations, but Set Operators offer a more concise and intuitive approach for specific tasks.
Conclusion
Set Operators in SQL provide a versatile option for data manipulation and analysis. Whether you need to combine, compare, or find differences in data, Set Operators offer desired solutions. By using best practices, you can use the full potential of SQL in your data management tasks. We hope you like this very well.
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