Function coalesce() merges multiple (≥2) columns of data into one column, by keeping the first left-most non-null value in each row and disgards the rest of values. Having all values null in one row without setting the default constant will make that row null ultimately.

When multiple columns are of different data types, data conversion might be triggered to guarantee a consistent data type in the final column.

Arguments：

• Any value <any>
• ...
• Default constant <any>

Returns：

• Merged value <any>

If some columns are non-homologous, Cartesian Product will be applied when the function is called in a WITH clause, or column length will be trimmed when called in a RETURN clause.

Comman Usage

Example: Find two products P001, P002 and two cards CA001 and CA002, return the product name or card number. Known that property @card.name does not exist

find().nodes({_id in ["P001", "P002", "CA001", "CA002"]}) as n
return coalesce(n.name, n._id)

Analysis: The non-existing property @card.name will return null when it is called, so _id will be returned for cards.

Example: Find all nodes, return the phone number, email address or MAC address, return 0 for nodes that have none of these properties. Know that the only related properties are @phone.number, @email.address and @device.MacAddress

find().nodes() as n
return coalesce(n.number, n.address, n.MacAddress, 0)