Write SOQL Queries

Challenge 5:

Create an Apex class that returns contacts based on incoming parameters.
For this challenge, you will need to create a class that has a method accepting two strings. The method searches for contacts that have a last name matching the first string and a mailing postal code matching the second. It gets the ID and Name of those contacts and returns them.
The Apex class must be called ContactSearch and be in the public scope
The Apex class must have a public static method called searchForContacts
The method must accept two incoming strings as parameters
The method should then find any contact that has a last name matching the first string, and mailing postal code (API name: MailingPostalCode) matching the second string
The method should finally return a list of Contact records of type List that includes the ID and Name fields

Solution:
public class ContactSearch {
    public static List<Contact> searchForContacts(String lName, String pCode){
        
        //use syntax to give refrence of paramameter name ex. :para_name
       return [SELECT Id, Name, LastName, MailingPostalCode
                                     FROM Contact
                                     WHERE LastName =:lName AND MailingPostalCode = :pCode];
    }

}

/*
 Let's view it line-by-line:

public class ContactSearch
This is just a class definition. Public says that this class is in public scope

public static List<Contact> searchForContacts(String lastName, String mailingPostalCode)
This is method declaration. Again, public keyword makes this method public accessible(public scope).
Static means that this method is class-method(static-method) and not instance-method. Difference is that for instance-method you would omit static keyword, but you would need an instance of that class to call this method.
List<Contact> is return type of the method. It means that this method will return a List of Contact objects.
searchForContacts is method name, use it to call this method.
String lastName, String mailingPostalCode are parameters that are expected by this method.
List<Contact> retList = [SELECT Id, Name, LastName, MailingPostalCode
                                 FROM Contact
                                 WHERE LastName = :lastName AND MailingPostalCode = :mailingPostalCode];

This line assigns the result of the query to retList variable.
List<Contact> retList makes a variable with name retList of type List<Contact>.
SELECT Id, Name, LastName, MailingPostalCode FROM Contact is a simple query that will return all contacts. However, you only need the ones that match given parameters, so the next line of the query is:
WHERE LastName = :lastName AND MailingPostalCode = :mailingPostalCode
This adds a filter to the query, so that it will only return results which match LastName and MailingPostalCode with given parameters.

Note the : in the query before the parameters:

If you want to use variables in your query, they should have : in front. That tells your code that it's not the value to be searched for, but a variable from the code

return retList; will return the list of matching contacts that you just found*/