Fetching the data from Database Server in JDBC

• Whenever we execute DQL Query, we get a result which is referred to as Resulatant or Processed Data.
•  The Processed or Resultant Data can be fetched by ResultSet Interface which is a part of JDBC API.
•   java.sql.ResultSet
• It is an interface which is a part of JDBC API and the implementations are provided by respective Database Server or vendors as a part of JDBC Driver.
•  A set of methods of ResultSet interface are used to fetch the Processes or Resultant data which are known as getXXX().
• There are two different methods which are overloaded methods present in a ResultSet Interface:-

   +XXX getXXX(int coloumnnumber/coloumnindex )  // ( coloumn number ---- coloumn index )

 

   +XXX getXXX(String coloumnname/coloumnlabel ) // ( coloumn name ----- coloumn label )

 If datatype is integer:-

  

  a) +int getInt(int coloumnnumber)

 

  b) +int getInt(String coloumnname)

 If datatype is String:-

  a) +String getString(int coloumnnumber)

 

  b) +String getString(String coloumnname)

 If datatype is Double:-

  a) +double getDouble(int coloumnnumber)

 

  b) +double getDouble(String coloumnname)

•  The return type of getXXX() method is the respective data-type.

• The return type of setXXX() method is void.

 // hasNext() --- next()  // Collection

 // next() --- getXXX()  // JDBC

 next():-

•  It is used to check whether the next record is present or not and returns a boolean value called true or false but not the record.

   + boolean next()

executeQuery():-

1.  It is a specialized method which is used to execute only DQL Queries.

2.  The outcome of a DQL is Processed or Resultant Data which can be fetched by ResultSet Interface which is a part of JDBC API.

3.  Hence, the Return type for executeQuery() is ResultSet interface.

4.  whenever we try to execute a DML query using this method it throws an exception called SQLException.

  Syntax:-

          +ResultSet executeQuery("Only DQL")

 

Implementation Object:-

  

        ResultSet rs = stmt.executeQuery(" DQL "); 

insert into thane.student values(1,'Oats',45.3); // Hard-coding

Oats -- Wheat

PlaceHolder:-

• It is a parameter which holds Dynamic values at the run time by the User.

•  In case of JDBC, place holder is represented by as " ? ".

Declaration of PlaceHolder in the Query:-

String inQry=" insert into thane.student values(?,?,?) ; // 1 - id  2 - name  3 - perc

String inQry1=" insert into thane.student values(?,?,?) ;

String upQry=" update thane.student set Product_Name = ? where id = ? ; //2 placeholders -- 2 times

String delQry=" delete from thane.student where id = ? ;

String selQry=" select * from thane.student where id = ? ;

Rules to set the data for a PlaceHolder:-

There are 3 different rules to set the data for PlaceHolder namely:-

1.  We have to set the data for a Placeholder before the execution.

2. The number of data must exactly match with the number of Placeholder.

3. We have to set the data for a Placeholder by using setXXX().

  +void setXXX(int placeholdernumber/placeholderindex, XXX data)

Ex:-

      sid=sc.nextInt();

     

        setInt(1, 15); // setInt(1, sid);

        setString(2, "Steve"); // setString(2, sc.next());

        setDouble(3, 34.5); // setDouble(3, sc.nextDouble());

 

• Tweet
• Share
• Share
• Share
• Share