QGIS/resources/function_help/coalesce

<h3>coalesce() function</h3>
Returns the first non-NULL value from the expression list.
<br>
This function can take any number of arguments.
<h4>Syntax</h4>
<code>coalesce(expression1, expression2 ...)</code><br>

<h4>Arguments</h4>
<code>expression</code> - any valid expression or value, irregardless of type.
<br>

<h4>Example</h4>
<!-- Show example of function.-->
<code>coalesce(NULL, 2) &rarr; 2</code><br>
<code>coalesce(NULL, 2, 3) &rarr; 2</code><br>
<code>coalesce(7, NULL, 3*2) &rarr; 7</code><br><br>
<code>coalesce("fieldA", "fallbackField", 'ERROR') &rarr; value of fieldA if it is non-NULL
 else the value of "fallbackField" or the string 'ERROR' if both are NULL</code><br>