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Update data in table

The thing i want to achieve here is that i have a table name total_product in mysql database and i want to retrieve the value of SNo = 1 from the table and update the Quantity in the table.
There is a text box i am using in GUI in which the additional product produced will be written.
The output from the table is stored in variable id and the new quantity that is produced is stored in the variable q1.
so the new product quantity will be q1 = q1 + id.
I am not able to understand what should i put in the sql statement that is used in stmt.executeUpdate(sql) because the sql is a string and i have to pass an integer value to Qunty in the sql string.
Please Help.
Connection conn = null ;
Statement stmt = null ;
String url = "jdbc:mysql://localhost:3306/project";
String user = "root";
String password = ".dpadpep";
try {
Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection(url,user,password);
String sql = "Select Qunty from total_product " + "where SNo = 1";
stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery(sql);
int id=0;
int q1 = Integer.parseInt(fld1[0].getText());
while(rs.next()) {
id = rs.getInt(1);
System.out.println("Quantity="+id);
}
q1 = q1+id;
sql = "UPDATE total_product " + "set Qunty = q1 where SNo=1";
stmt.executeUpdate(sql);

You don't need to explicitly retrieve the current value in the database, you can simply add the additional amount directly:
int q1 = Integer.parseInt(fld1[0].getText());
String sql = "UPDATE total_product SET Qunty = Qunty + ? WHERE SNo = 1";
PreparedStatement ps = conn.prepareStatement(sql);
ps.setInt(1, q1);
ps.executeUpdate();

Java - Sql query with Alias

I want to retrieve a particular column from the database. For a simple Select statement, I can able to able to retrieve a column like below
public String getDbColumnValue(String tableName, String columnName, String applicationNumber) {
String columnValue = null;
try {
PreparedStatement ps = null;
String query = "SELECT " + columnName + " FROM " + tableName +
" WHERE ApplicationNumber = ?;";
ps = conn.prepareStatement(query);
ps.setString(1, applicationNumber);
ResultSet rs = ps.executeQuery();
if (rs.next()) {
columnValue = rs.getString(columnName);
return columnValue;
}
}
catch (Exception ex) {
}
return columnValue;
}
But, I'm using alias in my query like below. And this query works fine. How to use this in Java to retrieve a particular column
select S.StatusDesc from application A, StatusMaster S
where A.StatusMasterId = S.StatusMasterId and A.ApplicationNumber = '100041702404'
Any help would be greatly appreciated!

I think you are confusing simple aliases, which are used for table names, with the aliases used for column names. To solve your problem, you can just alias each column you want to select with a unique name, i.e. use this query:
select S.StatusDesc as sc
from application A
inner join StatusMaster S
on A.StatusMasterId = S.StatusMasterId and
A.ApplicationNumber = '100041702404'
Then use the following code and look for your aliased column sc in the result set.
PreparedStatement ps = null;
String query = "select S.StatusDesc as sc ";
query += "from application A ";
query += "inner join StatusMaster S ";
query += "on A.StatusMasterId = S.StatusMasterId ";
query += "and A.ApplicationNumber = ?";
ps = conn.prepareStatement(query);
ps.setString(1, applicationNumber);
ResultSet rs = ps.executeQuery();
if (rs.next()) {
columnValue = rs.getString("sc");
return columnValue;
}
Note: I refactored your query to use an explicit inner join instead of joining using the where clause. This is usually considered the better way to write a query.

What's wrong with this SQL command?

I have a problem with a SQL Command.
I have a string that holds a SQL command, but when I run, it returns me an error: Column n1 does not exist Note: n1 is what I typed in my textField.
Code:
String nameprod tf_NameProd.getText = ();
         String sql = "select * from Product where prod_name =" + nameprod;//<-- this is my query
         iaeprod.Table(sql, tbl_Prod);
Any idea where I am missing?

You need to put single quotes around the string in your SQL. For example in your case it should be
"select * from Product where prod_name = '" + nameprod + "'";

String sql = "select * from Product where prod_name = '" + nameprod + "'";

because prod_name is a String use single quotes around the value
String sql = "select * from Product where prod_name ='" + nameprod+"'";
it will better to use prepared statement

Use this method instead:
Connection dbConnection = getDBConnection();
PreparedStatement stmt = null;
String nameProd = "select * from Product where prod_name = ?";
stmt = connection.prepareStatement(nameProd);
stmt.setString(1, tf_NameProd.getText() );
ResultSet rs = stmt.executeQuery();
P.S.: I haven't compiled this code. Please put try and catch statements at appropriate places

Use the value of a combo box in a SQL query

How can I use the value of a combo box in a SQL query with Java?
I try this code but it doesn't work.
String sql = " select * from table1 where ? like ?";
try{
pst = conn.prepareStatement(sql);
pst.setString(1, (String) jComboBox2.getSelectedItem());
pst.setString(2, txtsearch.getText() + "%");
rs = pst.executeQuery();}
If I use this code, it works.
String sql = " select * from table1 where Name like ?";
try{
pst = conn.prepareStatement(sql);
pst.setString(1, txtsearch.getText() + "%");
rs = pst.executeQuery();}

Well, you can do something like this:
try {
String sql = "select * from table1 where ";
sql += (String) jComboBox2.getSelectedItem();
sql += " like ";
sql += txtsearch.getText() + "%";
pst = conn.prepareStatement(sql);
rs = pst.executeQuery();
}

The place holder (?) is actually designed for the column values not for column/table name. Make use of string concatenation:
String sql = "select * from table1 where "
+ jComboBox2.getSelectedItem()
+" like ?";

Query JDBC Java

I have a problem with my java/jdbc code.
parameter index out of range (2 number of parameters which is 1)
Code:
Connection c = null;
MySQL MySQL = new MySQL(Host, Port, Database, Username, Password);
c = MySQL.open();
Player player = (Player) sender;
String zapytanie = "UPDATE `?` SET `tag`=? WHERE `name`='?';";
PreparedStatement ps = c.prepareStatement( zapytanie );
ps.setString(1, Tabel);
ps.setString(2, red);
ps.setString(3, player());
ps.executeUpdate(); //Executes the query
ps.close(); //Closes the query
c.close();

final String zapytanie = "UPDATE " + Table + " SET tag = ? WHERE name = ?";
No quotes around ? required
JDBC doesn't require a ; after any SQL statement
Place holders ? can only be used for column values