feat(UNIX_TIMESTAMP): add basic support for UNIX_TIMESTAMP function

[rtm-ctrlz]

Added basic support for UNIX_TIMESTAMP() function:

• without arguments: returns current timestamp
• with single argument: transforms string representation of date/datetime to timestamp

Things could be done:

• add some checks for invalid values/formats
• add support for timezones
• support for floating point type of return value

  mysql> SELECT UNIX_TIMESTAMP('2015-11-13 10:20:19.012');
      -> 1447431619.012
  

Docs for function - MySQL 8.0 Reference Manual

[sergiosalvatore]

Hi -- thanks for the submission! Would you be able to address the issues Psalm flagged?

[rtm-ctrlz]

@sergiosalvatore, I'm not sure that I know proper way to do it.

After $column = Evaluator::evaluate($conn, $scope, $args[0], $row, $result); line variable $column may have almost any type, so I see some ways:

• convert to string and let strtotime handle it;
• add check for type and pass only string, otherwise return NULL like original function do.

Also I'll add some things to this PR a bit later:

• fix for a typo (exception message)
• convertion false -> null for strtotime

[rtm-ctrlz]

Sorry, misclicked close button

[rtm-ctrlz]

@sergiosalvatore , have look, things done:

• fixed couple typos
• fixed psalm issue
• fixed return type to int | null , like original function
• with invalid values (when strtotime returns false) function will return NULL, like original function
• "refactored" from if's to switch for argument count check

[rtm-ctrlz]

bump ;)

[muglug]

Thanks!