Basic knowledge and usage of oracle query functions

Oracle is a very popular database management system that is widely used in enterprise-level applications and has many powerful functions and tools, such as query functions, that can be used to simplify the management and operation of the database.

Query function is a powerful tool in Oracle, which can help users query and retrieve data quickly and accurately. This article will introduce the basic knowledge and usage of query functions.

1. Definition of query function

The query function is a function of Oracle SQL language that is used to process data and return results. Query functions can perform queries in various ways, such as by comparing, calculating, or combining data. Query functions can also be used to filter, sort and group data. Oracle database provides many built-in query functions, such as AVG function, COUNT function, MAX function and MIN function. In addition to these built-in functions, users can also create their own query functions.

2. The basic syntax of the query function

The basic syntax of the query function is as follows:

SELECT function_name (expression)
FROM table_name
WHERE condition;

Among them, function_name represents the name of the function to be used, expression represents the data to be operated, table_name represents the name of the table to be queried, and condition represents the condition of the query.

For example, to calculate the average of a column in a table, you can use the following query function statement:

SELECT AVG(column_name)
FROM table_name
WHERE condition;

3. Common query functions

(1) AVG function: used to calculate the average of a column of values.

For example, to calculate the average of a column in a table, you can use the following query function statement:

SELECT AVG(column_name)
FROM table_name
WHERE condition;

(2) COUNT function: used to count the number of non-NULL values ​​in a column.

For example, to count the number of non-null values ​​in a column in a table, you can use the following query function statement:

SELECT COUNT(column_name)
FROM table_name
WHERE condition;

(3) MAX function: used to find the maximum value in a column.

For example, to find the maximum value in a column in a table, you can use the following query function statement:

SELECT MAX(column_name)
FROM table_name
WHERE condition;

(4) MIN function: used to find the minimum value in a column.

For example, to find the minimum value in a column in a table, you can use the following query function statement:

SELECT MIN(column_name)
FROM table_name
WHERE condition;

4. Example analysis

The following is an example of a query function. Suppose there is a table called "students" that contains students' grades. The following query function will find the average grade of all students with A grades:

SELECT AVG(grade)
FROM students
WHERE grade = 'A';

In this In the example, the AVG function is used to calculate the average grade of the selected students. The WHERE clause is used to filter out students with only A-level grades.

5. Summary

Query functions are an important part of the Oracle SQL language and can be used to query and retrieve data quickly and accurately. Oracle database provides many built-in query functions, such as AVG function, COUNT function, MAX function and MIN function, which can simplify operations on the database. In addition to these built-in functions, users can create their own query functions. By learning and mastering the basic syntax of query functions and common query functions, users can use Oracle database to manage and operate data more efficiently.

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