Basic usage analysis of DECODE function in Oracle

Basic usage analysis of DECODE function in Oracle

In Oracle database, DECODE function is a very commonly used function, used to implement functions similar to multi-layer if- Logical judgment and numerical replacement of else statements. The basic syntax of the DECODE function is as follows:

DECODE(expr, search1, result1, search2, result2, ..., default_result)

The meaning of the parameters is as follows:

• expr: The expression that needs to be judged
• search1, search2, ...: Indicates the value to be matched
• result1, result2, ...: Indicates The corresponding return result after successful matching
• default_result: Indicates the default return result if all search values ​​do not match successfully

The following is through some specific Code example to demonstrate basic usage of DECODE function.

Example 1: Basic Usage

Suppose there is an employee tableemployee, which contains the name of the employee and the year he joined. We want to determine the employee’s working years based on the year he joined. , and generate corresponding results.

SELECT name, 
       hire_year,
       DECODE(
           hire_year,
           2018, '工作1年',
           2017, '工作2年',
           2016, '工作3年',
           '工作3年以上') AS work_years
FROM employee;

In this example, the DECODE function matches based on the employee's entry year hire_year. If the employee's entry year is 2018, then '1 year of work' is returned. If the employee's entry year is 2017, Then return '2 years of work', and so on. If all search values ​​are not matched successfully, 'Working for more than 3 years' will be returned.

Example 2: Handling null values

Sometimes we need to handle some fields that may be empty, and the DECODE function can also be well applied to this situation.

Suppose there is a table product which contains the cost and selling price of products, we want to calculate the profit margin of each product and return 'loss' when the profit margin is negative .

SELECT product_id,
       cost,
       price,
       DECODE(
           price - cost,
           0, '无收益',
           NULL, '未知收益',
           (price - cost) / cost * 100
       ) AS profit_rate
FROM product;

In this example, the DECODE function matches based on the calculated profit margin, if the profit margin is 0, it returns 'No profit', if the profit margin is NULL, it returns 'Unknown profit', otherwise Returns the actual profit margin.

Example 3: Nested DECODE function

The DECODE function can be nested to achieve more complex logical judgments.

Suppose there is a table score, which contains students' scores, and we want to give corresponding ratings based on score segments.

SELECT student_id,
       score,
       DECODE(
           trunc(score/10),
           9, '优秀',
           8, '良好',
           7, '中等',
           6, '及格',
           '不及格'
       ) AS level
FROM score;

In this example, the DECODE function is used in a nested manner to determine the score range of the student's score at the first level, and then determines the corresponding rating at the second level.

In summary, the DECODE function is a very practical function in the Oracle database, which can easily implement complex logical judgments and numerical replacements. Through the examples in this article, I believe readers have a preliminary understanding of the basic usage of the DECODE function. I hope readers can flexibly use the DECODE function in practical applications to improve work efficiency.

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