Add new error class `QueryCanceled` which will be raised when canceling statement due to user request #31235
In MySQL, errno 1317 (
But in PostgreSQL,
So I decided to introduce new error class
…ng statement due to user request This changes `StatementTimeout` to `QueryCanceled` for PostgreSQL. In MySQL, errno 1317 (`ER_QUERY_INTERRUPTED`) is only used when the query is manually cancelled. But in PostgreSQL, `QUERY_CANCELED` error code (57014) which is used `StatementTimeout` is also used when the both case. And, we can not tell which reason happened. So I decided to introduce new error class `QueryCanceled` closer to the error code name.