Develop Reference

Java ResultSet Column count is always 1

I want to show the Column numbers of a table but it always shows the number 1. I have written the code below:
Class.forName(JDBC_DRIVER);
java.sql.Connection con=DriverManager.getConnection(DB_URL,USER,PASS);
try (Statement stmt = (Statement) con.createStatement()) {
String sql;
sql = "SELECT count(*) FROM information_schema.columns WHERE
table_name=\"my_b\"";
try (
ResultSet rs = stmt.executeQuery(sql)) {
int columCount = rs.getMetaData().getColumnCount();
System.out.println("Column number is: "+columCount);
}
stmt.close();
con.close();
Where is the error ?

First, you haven't needed Class.forName to load your JDBC drivers in a long time. Second, you are selecting a value but you are reading metadata. Third, when using try-with-resources you don't need explicit close calls (and your Connection should be closed in a finally, for example). Finally, use PreparedStatement and bind parameters. Like,
java.sql.Connection con = DriverManager.getConnection(DB_URL, USER, PASS);
String query = "SELECT count(*) FROM information_schema.columns WHERE table_name=?";
try (PreparedStatement stmt = con.prepareStatement(query)) {
stmt.setString(1, "my_b");
try (ResultSet rs = stmt.executeQuery()) {
if (rs.next()) {
int columCount = rs.getInt(1);
System.out.println("Column number is: " + columCount);
} else {
System.out.println("No rows");
}
}
} finally {
con.close();
}

You are not retrieving the result of the query, instead you are asking the result set metadata how many columns the result set has. And as your query only produce a single column (ie COUNT(*)), the result of ResultSetMetaData.getColumnCount() is 1, and that value is correct.
If you want to get the result of the query, you need to get it from the result set:
try (ResultSet rs = stmt.executeQuery(sql)) {
if (rs.next()) {
int columnsNumber = rs.getInt(1);
System.out.println("Column number is: "+columnsNumber );
}
}

The problem is that ResultSet.getColumnCount returns the number of columns in the query's result set, not the number of columns in a table.
If you are trying to get a count of columns on a table, the query you have is correct. You just need to retrieve the result of the query, rather than its metadata.
String sql = "SELECT count(*) FROM information_schema.columns WHERE table_name=\"my_b\"";
try (
ResultSet rs = stmt.executeQuery(sql));
rs.next();
int columCount = rs.getInt(1);
System.out.println("Column number is: " + columCount);
}

Class.forName(JDBC_DRIVER);
java.sql.Connection con=DriverManager.getConnection(DB_URL,USER,PASS);
try (Statement stmt = (Statement) con.createStatement()) {
String sql = "SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS WHERE table_schema = 'database_name' AND table_name = 'table_name'"
try (
ResultSet rs = stmt.executeQuery(sql)) {
//int columCount = rs.getMetaData().getColumnCount();
ResultSetMetaData rsmd = rs.getMetaData();
int columnsNumber = rsmd.getColumnCount();
System.out.println("Column number is: "+columnsNumber );
}
stmt.close();
con.close();

Try SELECT * FROM information_schema.columns WHERE table_name=\"my_b\"
Just omit the count(*) since this returns a single result, while you are looking for all columns.

Database Java Bean SQL Statement

In my database bean I have a section of code which is below :
public Integer getTotalOrgPoints() {
try {
PreparedStatement stmt = ConnectionHandler.getConnection().prepareStatement(QUERY_TOTAL_ORG_SCORE);
ResultSet rs = stmt.executeQuery();
while (rs.next()) {
totalOrgPoints = rs.getInt(1);
}
} catch (SQLException e) {
System.out.println(e.getMessage());
}
return totalOrgPoints;
}
For the statement QUERY_TOTAL_ORG_SCORE if I use
SELECT SUM(users.score)
FROM user_organisation_relationships
INNER JOIN users
ON user_organisation_relationships.user_id = users.id
WHERE organisation_id = 1
It will return the value for that organisation but if I use
SELECT SUM(users.score)
FROM user_organisation_relationships
INNER JOIN users
ON user_organisation_relationships.user_id = users.id
WHERE organisation_id = ?
I get nothing does anyone know why this is happening for me?.

Add this line to bind values for prepared statement before executequery
stmt.setInt(1, 1);
Modified:-
PreparedStatement stmt = ConnectionHandler.getConnection().prepareStatement(QUERY_TOTAL_ORG_SCORE);
stmt.setInt(1, 1);
ResultSet rs = stmt.executeQuery();

How to use select count on my database

private void Update_table(){
try {
String sql= "select Firstname, Lastname,ID_number from regmembers";
ps = conn.prepareStatement(sql);
rs = ps.executeQuery();
jTable_regMembers.setModel(DbUtils.resultSetToTableModel(rs));
jTable_regMembers.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
jTable_regMembers.getTableHeader().setReorderingAllowed(false);
jTable_regMembers.getTableHeader().setResizingAllowed(false);
} catch(Exception e){
JOptionPane.showMessageDialog(null, e+"");
}
}
how can i display the data of registered members of my database and put it into jtextfield, newbie question?

iterate over the resultset object and set the values obtained
ResultSet resultSet = ps.executeQuery();
if (resultSet.next()) {
do {
// perform your logic
yourTextfield.setText(rs.getString("yourColumnName"));
} while(resultSet.next());

You should be able to execute a simple query and use the value in the Result set to set your textfield.
String sql = "Select count(*) from regmembers";
ps = conn.prepareStatement(sql);
rs = ps.executeQuery();
textfield.setText(rs.getInt(1));
Hope this works the way you wanted it to

JDBC -- ResultSet values for column functions

How to get the outcome of the query-- the AVG(DIST).
MySQL is showing this result under the column "AVG(DIST)"-- no other clue.
How do i read this value from the ResultSet instance (rs in below code)?
PreparedStatement ps = c.prepareStatement("SELECT AVG(DIST) FROM POOL_TABLE");
ResultSet rs = ps.executeQuery();
ResultSet seems to be referring to them all by column names.
Not well-familiar to JDBC -- yet!
TIA.

You can use an alias name in the query and retrieve the value in any of the two ways.!
PreparedStatement ps = c.prepareStatement("SELECT AVG(DIST) AS AVERAGE_ALIAS FROM POOL_TABLE");
ResultSet rs = ps.executeQuery();
double avg = 0;
while (rs.next()) {
avg = rs.getDouble(1);
// OR
avg= rs.getDouble("AVERAGE_ALIAS");
}

Here it is:
double avg = 0;
while (rs.next()) {
avg = rs.getDouble(1);
}
Use alias if you have many aggregate functions in your query. See below answer!

PreparedStatement used for inserting of data,
i think you should use Statement.
Statement stmt = c.createStatement();
ResultSet rs = stmt.executeQuery("SELECT AVG(DIST) FROM POOL_TABLE");
if( rs.next() ){
System.out.print( rs.getString(1) );
}
i hope this example would help you :)

select few rows from resultset mysql java

i have used a select command in my java program and stored its value in the result set. now while looping in the resultset i want to use a select command which will select the first 5 lines of the resultset and insert into other table. for the second time, it should select the next 5 lines and insert into the table. and for the third time, so on..
Statement s = connection.createStatement();
s.executeQuery("Select * from table1");
ResultSet res = s.getResultSet();
while(res.next()){
// here i want to select the first 5 lines of the result set and insert in the second table
}

Statement s = connection.createStatement();
s.executeQuery("Select * from table1");
ResultSet res = s.getResultSet();
while(res.next()){
// here i want to select the first 5 lines of the result set and insert in the second table
while(res.next() && (res.getRow()%5) !=0){
//select from this table
//call insert method(what selected)
}
}

I would suggest changing your query using LIMIT and using a PreparedStatement. Something like:
SELECT * FROM table1 LIMIT ?,?
This has a couple of advantages:
You are not fetching everything in one shot - can be sometimes a performance benefit if you've a lot many rows to deal with in your table
You can change pre-define the number of elements that you want to fetch in every single batch
So your code will look something like this:
PreparedStatement ps = null;
ResultSet rs = null;
final int FETCH_LIMIT = 5; //number of elements to fetch per batch
final int BATCH_LIMIT = 3; //number of batches you would want
int currentRows = 0;
try{
ps = connection.prepareStatement("SELECT * FROM table1 LIMIT ?,?");
for(int currentBatch = 0; currentBatch < BATCH_LIMIT; currentBatch++){
ps.clearParameters();
ps.setInt(1, currentRows);
ps.setInt(2, currentRows + FETCH_LIMIT);
try{
rs = ps.executeQuery();
while(rs.next()){
// do your work
}
}catch(Exception exe){
//manage exception
}finally{
//manage resultset
}
currentRows += FETCH_LIMIT;
}
}catch(Exception exe){
//Handle your exception
}
finally{
//Manage your resources
}

Please add a falg and use that is it
int i=0;
while(res.next() && i< 5){
//select from this table
//call insert method(what selected)
i++;
}

Create another insert query dynamically inside the while loop and execute it outside the while loop