Introduction to types and functions of Oracle functions

Oracle SQL is a widely used relational database management system. Functions are a very important function when performing data processing. Oracle provides many different types of functions that can be used in SQL statements, providing powerful data processing capabilities. This article will introduce some commonly used Oracle function types and their functions, and provide specific code examples.

1. Aggregation function

Aggregation function is used to calculate the sum, average, maximum value, minimum value and other statistical information in the query result set. Commonly used aggregate functions include SUM, AVG, MAX, MIN, COUNT, etc. Here are some examples of commonly used aggregate functions:

-- 计算销售订单总金额
SELECT SUM(order_amount) AS total_amount
FROM orders;

-- 计算销售订单平均金额
SELECT AVG(order_amount) AS average_amount
FROM orders;

-- 统计订单数量
SELECT COUNT(*) AS total_orders
FROM orders;

2. Scalar functions

Scalar functions return a single value and can be used in SQL queries. Commonly used scalar functions include UPPER, LOWER, SUBSTR, TO_DATE, etc. The following are some examples of scalar functions:

-- 将字符串转换为大写
SELECT UPPER('hello') AS upper_str
FROM dual;

-- 将字符串转换为小写
SELECT LOWER('WORLD') AS lower_str
FROM dual;

-- 截取字符串的子串
SELECT SUBSTR('hello world', 1, 5) AS sub_str
FROM dual;

-- 将字符串转换为日期格式
SELECT TO_DATE('2022-01-01', 'YYYY-MM-DD') AS order_date
FROM dual;

3. Window function

Window function is used to perform aggregation operations within a specific window of the query result set. Commonly used window functions include ROW_NUMBER, RANK, DENSE_RANK, LEAD, LAG, etc. The following are some examples of window functions:

-- 对查询结果集进行编号
SELECT employee_id, salary, ROW_NUMBER() OVER (ORDER BY salary DESC) AS rank
FROM employees;

-- 计算员工薪水排名
SELECT employee_id, salary, RANK() OVER (ORDER BY salary DESC) AS salary_rank
FROM employees;

-- 计算部门内员工薪水排名
SELECT department_id, employee_id, salary, DENSE_RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) AS department_rank
FROM employees;

4. Conversion function

Conversion functions are used to convert types or formats of data. Commonly used conversion functions include TO_CHAR, TO_NUMBER, TO_DATE, etc. The following are some examples of conversion functions:

-- 将日期转换为字符串
SELECT TO_CHAR(order_date, 'YYYY-MM-DD') AS formatted_date
FROM orders;

-- 将字符串转换为数值
SELECT TO_NUMBER('123.45', '999.99') AS number_value
FROM dual;

-- 将字符串转换为日期
SELECT TO_DATE('2022-01-01', 'YYYY-MM-DD') AS order_date
FROM dual;

In actual database queries, the Oracle function types introduced above can help us process data more efficiently and improve the efficiency and accuracy of data processing. I hope this article will help readers understand the types and functions of Oracle functions.

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