ifnull()

Function ifnull() returns the left-most non null value from two values, or returns null if both values are null.

NOTE

When two values are of different data structures, data conversion might be triggered to guarantee a consistent data type in the final column.

NOTE

Occasions when null value is produced: properties not provided when inserting data, properties created after data is inserted, calling a property that is not existent.

Arguments：

• Value1 <any>
• Value2 <any>

Returns：

• Result <any>

Sample graph: (to be used for the following examples)

Run below UQLs one by one in an empty graphset to create graph data:

UQL
create().node_property(@default, "name").node_property(@default, "try1", int32).node_property(@default, "try2", int32).node_property(@default, "try3", int32)
insert().into(@default).nodes([{name:"Jason", try1:84}, {name:"Alice", try1:55, try2:79}, {name:"Lina"}, {name:"Eric", try1:39, try2:46, try3:61}, {name:"Pepe", try1:89}])

Common Usage

Example: Return the score of the last re-test that each student takes, knowing that each student has three chances, and retesting is allowed only if the previous one failed. Return null if a student does not give any try.

UQL
find().nodes() as n
return table(n.name, ifnull(n.try3, n.try2))

Result
| n.name | ifnull(n.try3, n.try2) |
|--------|------------------------|
| Jason  | null                   |
| Alice  | 79                     |
| Lina   | null                   |
| Eric   | 61                     |
| Pepe   | null                   |