Which set operator returns the combined rows from two queries without sorting or removing duplicates?

The set operators UNION, UNION ALL, INTERSECT, and MINUS can manipulate the result sets of two queries that specify the same number of columns in the Projection clause, and that have compatible data types in the corresponding columns of both queries.

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Set Operator

(The MINUS set operator has EXCEPT as its keyword synonym. Results that the MINUS and EXCEPT operators return from the same operands are always identical.)

These operators perform basic set operations of union, intersection, and difference on the result sets of two queries that are the left and right operands of the set operators:

The UNION set operator combines the qualifying rows from two queries into a single result set that consists of the distinct rows that either or both of the queries returned. (If you also include the ALL keyword, the UNION ALL result set can include duplicate rows.)
The INTERSECT set operator compares the result sets from two queries, but returns only the distinct rows that are in the result sets of both queries.
The MINUS set operator compares the result sets from two queries, but returns only the distinct rows in the result set of the left query that are absent from the result set of the right query.

The set operators are useful in business analytic contexts. They can also be used in SELECT statements to check the integrity of your database after you have performed a DML operation like UPDATE, INSERT, DELETE, or MERGE. The set operators can similarly be used when you transfer data to a history table, for example, when you need to verify that the correct data is in the history table before you delete rows from the original table.

All of the set operators have the same precedence. In complex queries that include more than one set operator, the precedence of operators is from left to right. Use parentheses to group set operators and their operands, if you need to override the default left-to-right precedence of set operators.

Only the UNION set operator supports the ALL keyword. The ALL keyword is not valid with the INTERSECT, MINUS, or EXCEPT set operators, from which only distinct rows are returned.

When comparing rows to calculate a set intersection or difference, two NULL values are considered equal in INTERSECT and MINUS operations.

The set operators UNION and UNION ALL can combine the result sets of two queries that specify the same number of columns in the Projection clause, and that have compatible data types in the corresponding columns of both queries.The set operators UNION, UNION ALL, INTERSECT, and MINUS can manipulate the result sets of two queries that specify the same number of columns in the Projection clause, and that have compatible data types in the corresponding columns of both queries.

The UNION operator returns the distinct results from both queries, excluding any duplicate rows.
The UNION ALL operator returns the all the qualifying rows from both queries, including any duplicate rows.

(The MINUS set operator has EXCEPT as its keyword synonym. Results that the MINUS and EXCEPT operators return from the same operands are always identical.)

These operators perform basic set operations of union, intersection, and difference on the result sets of two queries that are the left and right operands of the set operators:

The UNION set operator combines the qualifying rows from two queries into a single result set that consists of the distinct rows that either or both of the queries returned. (If you also include the ALL keyword, the UNION ALL result set can include duplicate rows.)
The INTERSECT set operator compares the result sets from two queries, but returns only the distinct rows that are in the result sets of both queries.
The MINUS set operator compares the result sets from two queries, but returns only the distinct rows in the result set of the left query that are absent from the result set of the right query.

Only the UNION set operator supports the ALL keyword. The ALL keyword is not valid with the INTERSECT, MINUS, or EXCEPT set operators, from which only distinct rows are returned.

When comparing rows to calculate a set intersection or difference, two NULL values are considered equal in INTERSECT and MINUS operations.

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This chapter describes the syntax and semantics of SQL statements that are recognized by HCL OneDB™.

The SQL statement names that appear as the title to each statement description in this chapter are listed in alphabetical order.

For some statements, important details of the semantics appear in other volumes of this documentation set, as indicated by cross-references.

For many statements, the syntax diagram, or the table of terms immediately following the diagram, or both, includes references to syntax segments in Data types and expressions or in Other syntax segments.

When the name of an SQL statement includes lowercase characters, such as SET Database Object Mode, it means that the first mixed-lettercase string in the statement name is not an SQL keyword, but that two or more different SQL keywords can follow the preceding uppercase keyword.

For an explanation of the structure of statement descriptions, see Overview of SQL syntax.

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The HCL OneDB™ Guide to SQL: Syntax describes the syntax of the statements, data types, expressions, operators, and built-in functions of the HCL OneDB dialect of the SQL language.

This information is intended for the following users:

Database users
Database administrators
Database security administrators
Database application programmers.

This information assumes that you have the following background:

A working knowledge of your computer, your operating system, and the utilities that your operating system provides
Some experience working with relational databases or exposure to database concepts
Some experience with computer programming.

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You can use the HCL OneDB™ implementation of the SQL language to develop applications for HCL OneDB database servers.

This article will provide a deep dive into the SQL Union operator, describing its many uses along with examples and explore some common questions like the differences between Union vs Union All.

To address real-world data requirements, we may need to combine result sets from multiple data sources so that we could do data analysis or create new datasets. The datasets may be identical but there are chances that they reference different tables. Is there a way to combine the data in a single query? Are Set Operators a viable option? Let’s get started and see how some of the existing operators can be used to help us address these common challenges.

In this article, we’ll review:

What a Set operator is
Union vs Union All and how they work
Discuss the rules for using Union vs Union All
SQL Operator Syntax
How to use simple SQL Union clause in the select statement
How to use SQL Union with the queries that have the WHERE clause
How to use the SELECT INTO clause with Union
How to use SQL Union with the queries that have a WHERE clause and order by clause
How to use SQL Union and SQL Pivot
How to use SQL Union with GROUP and HAVING clauses

Operators

An operator is a symbol or a keyword defines an action that is performed on one or more expressions in the Select statement.

Set Operator

Let’s get into the details of Set Operators in SQL Server, and how to use them

There are four basic Set Operators in SQL Server:

Union
Union All
EXCEPT
INTERSECT

Union

The Union operator combines the results of two or more queries into a distinct single result set that includes all the rows that belong to all queries in the Union. In this operation, it combines two more queries and removes the duplicates.

For example, the table ‘A’ has 1,2, and 3 and the table ‘B’ has 3,4,5.

The SQL equivalent of the above data is given below

In the output, you can see a distinct list of the records from the two result sets

Union All

When looking at Union vs Union All we find they are quite similar, but they have some important differences from a performance results perspective.

The Union operator combines the results of two or more queries into a single result set that includes all the rows that belong to all queries in the Union. In simple terms, it combines the two or more row sets and keeps duplicates.

For example, the table ‘A’ has 1,2, and 3 and the table ‘B’ has 3,4,5.

The SQL equivalent of the above data is given below

In the output, you can see all the rows that include repeating records as well.

INTERSECT

The interest operator keeps the rows that are common to all the queries

For the same dataset from the aforementioned example, the intersect operator output is given below

The SQL Representation of the above tables

The row ‘3’ is common between the two result sets.

EXCEPT

The EXCEPT operator lists the rows in the first that are not in the second.

For the same dataset from the aforementioned example, the Except operator output is given below

The SQL representation of the above tables with EXCEPT operator is given below

SELECT 1 [Non-Common from only A ]

List the non-common rows from the first set.

Note: It is very easy to visualize a set operator using a Venn diagram, where each of the tables is represented by intersecting shapes. The intersections of the shapes, where the tables overlap, are the rows where a condition is met.

Syntax:

The syntax for the Union vs Union All operators in SQL is as follows:

SELECT Column1, Column2, … ColumnN FROM <table> [WHERE conditions] [GROUP BY Column(s]] [HAVING condition(s)] UNION SELECT Column1, Column2, … ColumnN FROM table [WHERE condition(s)];

ORDER BY Column1,Column2…