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 the MINUS keyword. The MINUS operator 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, the SELECT statement is used to specify the columns that need to be retrieved and tables, the FROM keyword is used to specify the data source, and the MINUS keyword is used to perform the subtraction operation.

3. Example of subtraction operation

Suppose we have two tables table1 and table2, 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 in table2 from table1 to 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, only is left in the result. Data in table1 that is not in table2.

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 execute table2 and table3 joint query, and then use the result as a subquery for the subtraction operation to obtain the difference set of table1 relative to table2 and table3.

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!

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