Support Native Flink UNIX_TIMESTAMP Function #1863
Description
The Flink UNIX_TIMESTAMP UDF is a commonly used user-defined function.
UNIX_TIMESTAMP has multiple usage methods.
- 0 inputs：Gets current Unix timestamp in seconds. This function is not deterministic which means the value would be recalculated for each record.
- 1 inputs：Converts a date time string string1 with default format 'yyyy-MM-dd HH:mm:ss' to Unix timestamp (in seconds).
- 2 inputs：Converts a date time string string1 with format string2 to Unix timestamp (in seconds).
Notes: In Java, the date format is 'yyyy-MM-dd HH:mm:ss', but in Rust it is '%Y-%m-%d %H:%M:%S', to ensure compatibility with Flink scenarios, we need to convert the format.