Update sql.md

Fix the parameter type to the correct type

Author: Kalmaegi

content/techniques/sql.md

@@ -180,7 +180,7 @@ export class UsersService {
     return this.usersRepository.find();
   }
 
-  findOne(id: string): Promise<User> {
+  findOne(id: number): Promise<User> {
     return this.usersRepository.findOneBy({ id });
   }