JDBC_notes

How do you connect to database using Java ? 
We use JDBC API comes with JDK  
In order to connect to a specific Relational Database management system , we need to have a driver of that database vendor like oracle, mysql , postgress , MariaDB .,.,........
what is a JDBC driver : It's a jar file that contains packages and classes and it has implementation of JDBC standard 
There are 3 major interface that used to programatically access database 
---  all these interfaces are coming from 
   java.sql package 
Connection ,
     we use DriverManager and connection String , database credentials to make connection 
    Connection conn = DriverManager.getConnection(connection_str,db_user,db_password);
Statement , 
     we can create statement object using connection object, it has ability to executeQuery
      Statement stmt = conn.createStatement();
ResultSet 
     Once statement object query is executed , it will result in a ResultSet object that store entire result, 
     ResultSet rs = stmt.executeQuery("SELECT * FROM REGIONS");
     rs.next()  to move to first row 
Eech resultset can contain 1 result of the query run 
if you want to run another sql query ,create another ResultSet Object 
ResultSet object has few usueful methods to move your cursor around , so we can get correct data from the row we are interested in 
    -- by default your cursor is at beforeFirst location 
rs.next()   move cursort to next location 
rs.previous(); move cursor to previous location 
    -- ResultSet must be TYPE_SCROLL_INSENSITIVE 
rs.absolute(2); move cursor to specific row 
rs.first(); // move the cursor to first row
rs.last(); // move the cursor to last row
rs.beforeFirst(); // move the cursor to the location right before first row
rs.afterLast(); // move the cursor to the location right after last row
How do we read data by column name regardless of data type : 
        rs.getObject("column_name_here") ;