nvl usage in mysql

The NVL function in MySQL is used to replace NULL values ​​with specified default values. The syntax is NVL(expression, default_value). It can be used to: 1. Replace NULL values ​​to avoid queries returning incomplete rows; 2. Fill in missing data for calculation or analysis; 3. Unify NULL values ​​to a specific value when comparing or sorting. For example, NVL(name, 'Unknown Name') replaces a NULL name with "Unknown Name".

NVL function in MySQL

What is the NVL function?

The NVL function is a MySQL database function that replaces NULL values ​​with a specified default value.

Syntax:

<code>NVL(expression, default_value)</code>

• expression: The expression to be checked, which can be a column name, a constant or a subquery.
• default_value: The default value to be returned when expression is NULL.

How to use the NVL function?

The NVL function can be used in the following scenarios:

• Replace NULL values ​​to avoid queries returning incomplete rows.
• Fill in missing data for calculation or analysis.
• Uniform NULL values ​​to a specific value when comparing or sorting.

Example:

<code class="sql">SELECT NVL(name, 'Unknown Name') FROM customers;</code>

This will return the names of all customers, if a customer's name is NULL, replace it with the string "Unknown Name" .

Note:

• The default value can be any type of data, but it must be compatible with the type of expression.
• If expression itself is not NULL, the NVL function returns the original value of expression.
• The NVL function does not modify the actual value in the table, it only returns the replaced value.

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