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Lesson 4 UNION, INTERSECT, and MINUS
Objective Compare the INTERSECT, MINUS, and UNION commands.
How do you combine the results of two separate queries? Oracle provides three commands, UNION, INTERSECT and MINUS, that handle combining query results in three different ways.
Command Description
UNION The most commonly used command, UNION combines the two answer sets into a single answer set. It automatically removes duplicate rows from the results.
INTERSECT INTERSECT gives you the rows that are found in both queries by eliminating rows that are only found in one or the other query.
MINUS MINUS gives you the rows that are found in the first query and not in the second query by removing from the results all the rows that are found only in the second query.


Differences between commands
The following animation shows you the difference between these three commands by using two circles to represent two query result sets, labeled A and B. The animation shows which portions of the two result sets are returned by combining the two queries with each of the three set commands: INTERSECT, then UNION, then MINUS.
INTERSECT, then UNION, then MINUS commands
Command rules
There are two important rules to follow when using these commands:
  1. Both queries must have matching lists of columns with matching datatypes. In other words, if your first query returns three columns, a date, a number, and a character column, your second query must also return three columns: a date, a number, and a character column, in that order. The two queries do not need to use the same column names.
  2. The first query's list of columns is used for the final results set. If two corresponding columns in the two queries have different lengths, the first query is used to set the length of the final results set. If the second query's column is longer, you may get an error in your results due to data truncation.

Here is an example of two queries connected with the INTERSECT command:
SELECT TO_CHAR(LAST_UPDATE_DATE,'YYYY-MM'), 
 UPDATED_BY_USER
FROM PRODUCT
INTERSECT
SELECT TO_CHAR(LAST_UPDATE_DATETIME,'YYYY-MM'), 
 CREATED_BY_USER
FROM PET_CARE_LOG
ORDER BY 1
This query finds the dates (year and month only) and the employee names that are the same for changes made to the PRODUCT table and log entries made to the PET_CARE_LOG.
In the next lesson, you will learn how to use advanced set operators.
Intersect union minus Operations
Click the link below to read about the intersect, union, and minus operations used in Oracle.
Intersect union minus Operations