Oracle database operation skills: detailed explanation of subtraction operation

As a powerful relational database management system, Oracle database provides a wealth of computing operations to meet user needs. In daily database operations, subtraction operation is a common and important operation. It can help us realize the subtraction operation of data to obtain the results we need. This article will discuss in detail the techniques related to subtraction operations in Oracle database, and give specific code examples to help readers better understand and use this function.

1. The basic concept of subtraction operation

In Oracle database, the subtraction operation is implemented through theMINUSkeyword. TheMINUSoperator is used to select all rows from the first query result that are not in the second query result, that is, to find the difference between the two result sets. Through subtraction operations, we can quickly filter out data that meets specific conditions and further analyze and process the data.

2. The syntax of the subtraction operation

The syntax of the subtraction operation is as follows:

SELECT column1, column2, ... FROM table1 MINUS SELECT column1, column2, ... FROM table2;

Among them, theSELECTstatement is used to specify the columns that need to be retrieved and tables, theFROMkeyword is used to specify the data source, and theMINUSkeyword is used to perform the subtraction operation.

3. Example of subtraction operation

Suppose we have two tablestable1andtable2, their structures are as follows:

table1: id | name 1 | Alice 2 | Bob 3 | Charlie table2: id | name 2 | Bob 3 | Charlie 4 | David

We want to subtract the data intable2fromtable1to get the difference set. We can execute the following SQL query:

SELECT id, name FROM table1 MINUS SELECT id, name FROM table2;

After executing the above query, we will get the following results:

id | name 1 | Alice

As you can see, according to the definition of the subtraction operation, onlyis left in the result. Data in table1that is not intable2.

4. Extended example of subtraction operation

In addition to simple two-table subtraction operations, we can also perform more complex subtraction operations through subqueries, joint queries, etc. For example, we can use subqueries to implement subtraction operations on multiple tables. The example is as follows:

SELECT id, name FROM table1 MINUS ( SELECT id, name FROM table2 UNION SELECT id, name FROM table3 );

In the above example, we first executetable2andtable3joint query, and then use the result as a subquery for the subtraction operation to obtain the difference set oftable1relative totable2andtable3.

Conclusion

Through the above introduction and examples, I believe that readers will have a deeper understanding of the subtraction operation in Oracle database. Subtraction operation is a common and practical operation in database queries, which can help us process data efficiently and obtain the results we want. In practical applications, readers can flexibly use subtraction operations according to specific business needs to improve the efficiency and accuracy of database queries. I hope this article is helpful to readers, thank you for reading!

The above is the detailed content of Oracle database operation skills: detailed explanation of subtraction operation. For more information, please follow other related articles on the PHP Chinese website!