Questions about database insertion

Database insertion problem PHPcode $ SQL = & quot; insertintomsg (id, userid, contant, oppeardate) values ('', '2013', '$ _ POST [contant]', now () & quot; see this in the tutorial. now () inserts the current time into the database.

PHP code

  $ SQL = "insert into msg (id, userid, contant, oppeardate) values ('', '000000', '$ _ POST [contant]', Now ())";

As mentioned in the tutorial, now () inserts the current time, but I use print $ SQL to find that the output is now (), not the current time, the format is incorrect when the database is inserted. do you have any idea why?

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$ SQL = "insert into msg (id, userid, contant, oppeardate) values ('', '000000', '$ _ POST [contant]', Now ())";

Now is executed in mysql. what is the use of print $ SQL in php?
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Set names gbk;
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The php date () function can also obtain the current timestamp.
In my opinion, you can get the current time in PHP and insert it as a variable.