The lookup database cannot be found after PHP value is transferred

The lookup database cannot be found after PHP value is passed
To do a simple student management system
Professional: Computer Science and TechnologyNetwork EngineeringFinancial managementAll above is the option here is the database search if ($pro! = "All") {$query = "select * from S where pro= $pro";} Excuse me, but why did you remove the value but can't find a match in the database? Prompt for query to null value the database already has this data------solution--------------------at least this $query = "SELECT * from S where pro= ' $ Pro ' "; 