What does coalesce in sql mean?

The COALESCE function returns the expression of the first non-null value in a list. Its syntax is COALESCE(expression1, expression2, ..., expressionN), and the parameter is the expression to be checked for NULL. Returns an expression whose value is the first non-null value in the list, or NULL if there is no non-null value. It can be used to handle NULL values ​​in different expressions and ensure that a non-null value is returned.

COALESCE function in SQL

What is the COALESCE function?

COALESCE is a SQL function used to handle NULL values. It returns the first non-null expression in a list.

Syntax:

##COALESCE(expression1, expression2, ..., expressionN)

Parameters:

expression1, expression2, ..., expressionN: Expression to check whether it is NULL.

Return value:

The expression of the first non-null value in the list. If there is no non-null value, NULL is returned.

Usage example:

Suppose we have a table named "Customers" that contains the "Name" and "Email" columns:

<code class="sql">SELECT Name, COALESCE(Email, 'Unknown Email')
FROM Customers</code>

This query will return the name of each customer, or "Unknown Email" if the customer does not have an email address.

Other examples:

• COALESCE(FirstName, LastName): If FirstName is NULL, return LastName; otherwise, return FirstName .
• COALESCE(Price, DefaultPrice): If Price is NULL, return DefaultPrice; otherwise, return Price.

Note:

The COALESCE function can accept any number of expressions.
• If all expressions are NULL, the COALESCE function returns NULL.
• The COALESCE function performs strict comparisons on NULL values. That is, you cannot use COALESCE to compare NULL and empty strings.

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