[FLINK-24385] Add TRY_CAST function to be able to handle errors

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.15.0
• Component/s: Table SQL / API
• Labels: pull-request-available
• Assignee: Marios Trivyzas
• Reporter: Marios Trivyzas
• Created: 27/Sep/21 08:22
• Updated: 16/Feb/22 17:12
• Resolved: 16/Feb/22 17:12

Description

Currently, CAST is returning null when the conversion requested fails, whereas normally in SQL it would just throw an error. Maybe it would be better to change the implementation of CAST to throw errors on failed conversions, and introduce TRY_CAST which would return null in such cases. Then with a simple wrapping of a TRY_CAST expression with COALESCE the user can also use an alternative default value to be returned instead of null. e..g:

}}{{SELECT COALESCE(TRY_CAST(col1 AS INT),  -1) FROM test

Issue Links

• blocks: FLINK-26125 Doc overhaul for the CAST behaviour
• links to: GitHub Pull Request #18611