If mysql exists, it is updated. if mysql does not exist, it is inserted. how can this problem be written?

If mysql exists, it is updated. if it does not exist, it is inserted. how can I write it? if mysql exists, it is updated. if it does not exist, it is inserted, how can I write a table like friend_idcomment_num, which records comments on Friends? when this data exists, it is directly Updated. if it does not exist, insert it first. what can I do? thank you, PHPcodeREPLACE mysql is updated if it exists. if it does not exist, it is inserted. how can I write it?
Mysql is updated if it exists. if it does not exist, it is inserted. how can I write it?
Such as a table that records comments on friends
Friend_id comment_num
If this data entry exists, it is directly Updated. if it does not exist, insert it first. how can this problem be solved? thank you.

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PHP code

Replace into 'Table' (friend_id, comment_num) VALUES (...);
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If an old record in the table has the same value as a new record used for the primary key or a UNIQUE index, the old record is deleted before the new record is inserted.
Unless the table has a primary key or UNIQUE index, it makes no sense to use a REPLACE statement.


  

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PHP code

   
Replace into 'Table' (friend_id, comment_num) VALUES (...);

   
Record modified and inserted