In mysql, what is the meaning of: id and ': ID' => $ orderid?

In mysql, what is the meaning of: id and: id & gt; $ orderid? $ Agentid = pdo_fetchcolumn ('select agentid from '. tablename ('shop _ order ').' Where id =: idLimit 1', array (
': ID' => $ orderid
));

In mysql, what does id =: id and ': ID' => $ orderid mean?

: Is id a placeholder?
$ Orderid is a parameter?

Reply to discussion (solution)

SQL command select agentid from '. tablename ('shop _ order'). 'where id =: id limit 1
In: id is the parameter name of parameterized expression

The second parameter array (': ID' => $ orderid)
In: id is to replace the parameter name: id with the real variable $ orderid

SQL command select agentid from '. tablename ('shop _ order'). 'where id =: id limit 1
In: id is the parameter name of parameterized expression

The second parameter array (': ID' => $ orderid)
In: id is to replace the parameter name: id with the real variable $ orderid

Can this be used only in mysqli?

Both mysqli and PDO can be used.

MySQL itself supports parameterized query
But php_mysql extensions are not supported.