In-depth understanding of the functions and characteristics of Oracle DECODE function

In-depth understanding of the functions and characteristics of the Oracle DECODE function

In the Oracle database, the DECODE function is a very commonly used conditional judgment function. Its function is based on specified conditions. Perform numerical conversion or return a fixed value. In actual database applications, the DECODE function can help us process data quickly and flexibly, and improve the efficiency of data query and analysis. Next, we will delve into the functions and characteristics of the Oracle DECODE function and illustrate it with specific code examples.

1. The syntax of the DECODE function

The basic syntax of the DECODE function is as follows:

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

Among them, expr is the expression to be compared, search1, search2, etc. is the value used for comparison, result1, result2, etc. are the returned results, and default is the default return value when all comparison values ​​do not match.

2. Function and characteristics of DECODE function

DECODE function is mainly used to judge multiple conditions on a single expression. Its characteristics are as follows:

## The #DECODE function can only be used in SELECT statements or PL/SQL statements, and cannot be used in WHERE clauses or GROUP BY clauses.
The DECODE function can use various data types such as text, numbers, dates, etc. for comparison.
The return value type of the DECODE function is the same as the data type of the first result parameter.
The comparison of the DECODE function is performed sequentially. Once the condition is matched, the corresponding result will be returned immediately, and subsequent conditions will not be compared.

Specific code examples of the DECODE function

SELECT emp_name, DECODE(emp_level, 'A', '高级', 'B', '中级', 'C', '初级', '未知') AS salary_level
FROM employees;

SELECT stu_name, DECODE(score >= 60, 1, '及格', 0, '不及格') AS pass_status
FROM students;

SELECT product_name, DECODE(sales_volume, 0, '无销售', 1, '低', 2, '中', 3, '高', '未知') AS sales_level
FROM products;

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