How does discuzX2.5 write a page to directly operate on database tables?

How does discuzX2.5 write a page to directly operate database tables? I have a requirement to execute SQL statements directly. how can I write code? ------ Solution ------------------ One is that you use the mysql function provided by PHP to directly execute one is that you find the file defining IN_DISCUZ, including, or you can define how to write a page on discuz X2.5 to directly operate the database table?
I have a requirement to execute SQL statements directly. how can I write code?

------ Solution --------------------
One is to directly execute the mysql function provided by PHP.
One is that you find the file defining 'in _ discuz', including it, or you can define this constant yourself.