Common Errors ============= String concatenation -------------------- In AQL, strings must be concatenated using the [CONCAT()](Functions/String.md#concat) function. Joining them together with the `+` operator is not supported. Especially as JavaScript programmer it is easy to walk into this trap: ```js RETURN "foo" + "bar" // [ 0 ] RETURN "foo" + 123 // [ 123 ] RETURN "123" + 200 // [ 323 ] ``` The arithmetic plus operator expects numbers as operands, and will try to implicitly cast them to numbers if they are of different type. `"foo"` and `"bar"` are casted to `0` and then added to together (still zero). If an actual number is added, that number will be returned (adding zero doesn't change the result). If the string is a valid string representation of a number, then it is casted to a number. Thus, adding `"123"` and `200` results in two numbers being added up to `323`. To concatenate elements (with implicit casting to string for non-string values), do: ```js RETURN CONCAT("foo", "bar") // [ "foobar" ] RETURN CONCAT("foo", 123) // [ "foo123" ] RETURN CONCAT("123", 200) // [ "123200" ] ```