How to use coalesce function in oracle

Oracle COALESCE function returns the first non-null value in a set of expressions and is often used for data processing and repairing missing values. Usage: 1. Determine the expression to be checked; 2. Specify the COALESCE function; 3. Provide the expression to be checked. This function accepts any number of expressions as parameters and returns the first non-null value, or NULL if all expressions are null.

Oracle COALESCE Function Usage

The COALESCE function is a built-in function that returns the The first non-null value. It is very useful in data processing and fixing missing values.

Syntax

<code>COALESCE(expr1, expr2, ..., exprN)</code>

Where:

• expr1, expr2,..., exprN is the expression to be checked, which can be a column , function or constant.

Usage

To use the COALESCE function, follow these steps:

1. Determine the expression to check Formula: Select a set of expressions to check for missing values.
2. Specify the COALESCE function: Use the COALESCE function in a query or statement.
3. Provide the expression to check: Pass the expression to check as a parameter to the COALESCE function.

Example

<code>SELECT COALESCE(name, 'Unknown') FROM customers;</code>

This query will return the value of the name column in the customers table. If the name column is null or an empty string, the COALESCE function returns an 'Unknown' string.

Note:

• The COALESCE function returns the first non-null value. Therefore, if all expressions are NULL, the COALESCE function returns NULL.
• The COALESCE function can accept any number of expressions as parameters.
• The COALESCE function is useful for filling in missing values ​​or aggregating values ​​from multiple data sources.

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