Talk about oracle query function

Foreword:

In Oracle database, data query is a very frequent operation, so some efficient query plans and functions are one of the knowledge that database developers must master. This article will introduce the relevant knowledge of Oracle query functions, hoping to provide readers with reference and help.

Text:

In the Oracle database, we often need to perform various query operations, but if we have to query the entire table every time, it will take a long time due to querying a large amount of data. The overhead is relatively high. Therefore we need some efficient query functions to solve this problem.

1. MAX() function

The MAX() function is used to query the maximum value of a column. Its syntax format is:

SELECT MAX( column_name) FROM table_name;

For example, we have a "Score" table, which has a "score" column. We want to query the maximum value of the "score" column in this table, then we can use the following code:

SELECT MAX(score) FROM Score;

2. MIN() function

The MIN() function is used to query the minimum value of a column. The syntax format is similar to the MAX() function, as follows:

SELECT MIN(column_name) FROM table_name;

For example, we have a "Score" table, which has a "score" column, we want to query the minimum value of the "score" column in this table, then we can use the following code:

SELECT MIN(score) FROM Score;

3. COUNT() function

The COUNT() function is used to count the number of rows in a table or the number of records in a certain column. The syntax format is as follows:

SELECT COUNT(*) FROM table_name;

SELECT COUNT(column_name) FROM table_name;

"" means all columns, if query table If you want to query the total number of rows in all columns, you can use SELECT COUNT(); if you want to query the number of records in a certain column, you can use SELECT COUNT(column_name).

For example, we have a "Score" table. If you want to query the number of records in all columns in this table, you can use the following SQL statement

SELECT COUNT(*) FROM Score;

If you want to query the number of records in the "score" column in the "Score" table, you can use the following SQL statement

SELECT COUNT(score) FROM Score;

4. SUM() function

The SUM() function is used to calculate the sum of the values ​​​​of a certain column. Its syntax format is as follows:

SELECT SUM(column_name) FROM table_name;

For example, we have a "Score" table with a "score" column. If we want to query the sum of the "score" columns in this table, we can use the following code:

SELECT SUM( score) FROM Score;

5. AVG() function

The AVG() function is used to query the average value of a certain column. Its syntax format is as follows:

SELECT AVG(column_name) FROM table_name;

For example, we have a "Score" table, which has a "score" column, and we want to query the average value of the "score" column in this table, then You can use the following code:

SELECT AVG(score) FROM Score;

Summary:

This article introduces the relevant knowledge of Oracle query functions and lists MAX() function, MIN() function, COUNT() function, SUM() function and AVG() function. These functions can quickly collect statistics in queries and improve query efficiency. We hope they will be helpful to readers in their study and work.

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