What does nvl mean in sql

The NVL function in SQL is used to replace the NULL value with the specified default value, and the syntax is NVL(expression, default_value). It is used to avoid errors or exceptions caused by NULL values, provide meaningful default values, and ensure that queries return non-NULL values. It should be noted that default_value must be of the same data type as expression, and NVL will not modify the original value. For complex expressions, you can use nested NVL functions to handle multiple NULL values, but for large data sets, it is recommended to use NVL only when needed to avoid performance degradation.

The meaning of NVL in SQL

NVL is a function in SQL, which is used to replace the NULL value with The specified default value.

Syntax

##NVL(expression, default_value)

Where:

expression: The expression to check.
• default_value: The value returned if expression is NULL.

Example

The following example replaces NULL values ​​with "Unknown":

SELECT NVL(name, 'Unknown') FROM customers;

How it works

The NVL function first checks whether expression is NULL. If NULL, returns default_value. If expression is not NULL, returns the value of expression.

Purpose

NVL functions are useful in the following situations:

To avoid errors or exceptions caused by NULL values.
• Provide meaningful default values ​​for reports or displays.
• Ensure that queries always return non-NULL values.

Things to note

default_value must be the same data type as expression.
• NVL does not modify the original value, it only returns a replaced value.
• For complex expressions, nested NVL functions can be used to handle multiple NULL values.
• For large data sets, using NVL may cause performance degradation, so it is recommended to only use it when needed.

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