Ask a question about the mysql_query function

I want to teach you a question about the mysql_query function. to do this, set @ mycnt = 0; select (@ mycnt: = @ mycnt + 1) asrank, nick_name, total_scores, start_time, expire asks for a question about the mysql_query function.
Used for ranking
Set @ mycnt = 0;
Select (@ mycnt: = @ mycnt + 1) as rank, nick_name, total_scores, start_time, expire_time from of_user_exam left join of_user_basic on limit = Sort order by-total_scores, expire_time;
There are two such sentences, but they cannot be executed using mysql_query in a single string. Is there any other way to get the result?

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What is the meaning of mycnt? if it is a sequence number like 1, 2, 3, 4, 5, 6, 7, 8, why should it be in an SQL statement?