Reference: Try Expression

A try(...) expression allows graceful error handling in case of invalid inputs. Instead of raising an error that terminates the query, CedarDB returns null.

Example

Casts between different data types are a common source of errors. For example, the following cast raises an error:

with input(str) as (values ('42'), ('oops'))
select str::int from input;

ERROR:  invalid number format for integer: no digits found in "oops"

Wrapping the cast in a try expression masks the error and returns null instead:

with input(str) as (values ('42'), ('oops'))
select try(str::int) from input;

  try
--------
     42
 <null>
(2 rows)

Try expressions work for many common errors, and can catch more than one error condition:

with input(str) as (values ('1'), ('0'), ('oops'))
select try(1::numeric / str::int) from input;

   try
----------
 1.000000
   <null>
   <null>
(3 rows)

try catches errors that the wrapped expression raises while processing a row, for example:

• Invalid input in casts, such as 'oops'::int, '2024-13-45'::date, or '{bad'::jsonb
• Division by zero, including modulo (%)
• Numeric overflow, such as 2147483647 + 1 or 100000::smallint

Errors from mathematical functions with invalid arguments, such as ln(0) or sqrt(-1) on column values, are not caught and still terminate the query. Errors that are not raised by the wrapped expression itself, such as a scalar subquery that returns more than one row, are not caught either.