We Keep Coding

Insert new Value in MySQL in same Cloumn (Java/Code)

I am working on a little project.
Now I don't know, how to "replace" a old value in the mysql table.
Here you can see the table:
Thats my methods:
MySQL.update("INSERT INTO OnlineServer (Name) VALUES ('" + API.getServerFreeServer() + "');");
public static void update(String qry) {
try {
java.sql.Statement st = con.createStatement();
st.executeUpdate(qry);
st.close();
} catch (SQLException e) {
connect();
e.printStackTrace();
}
}
The problem now is, if I update the mysql, it dont replace the value in the column "Name". It just add a new Value under the old Value. The table is Going to be too huge if I Update every 5 seconds.
I need exactly one value in the column "Name".
So I have tryed to replace the insert but it doesn't work for me.
Maybe you have some ideas?
Sorry for my bad English, I'am German.

It sounds like you want to do an update here of the table, rather than an insert:
String sql = "UPDATE OnlineServer Set Name = ?";
PreparedStatement ps = dbConnection.prepareStatement(sql);
ps.setString(1, API.getServerFreeServer());
ps.executeUpdate();
By the way, your current query is doing raw string concatenation, making it prone to typos as well as SQL injection. I have used a prepared statement above, which is the most desirable way to execute a query using JDBC.

INSERT operation is for adding new record only and thus irrespective of you specify single column or 1million column it will add a new record. You actually need an UPDATE statement saying
UPDTE OnlineServer SET Name = <value>
You might also want to check INSERT ... ON DUPLICATE KEY UPDATE

Why does this Query return NULL?

I have a derby users database which I query, when the user clicks login on the application.
However, when I query the users table with the parameter [user] derby returns a null Object instead of the record it ought to return.
Here is my code:
String ssql = "SELECT * FROM USERS WHERE UNAME LIKE ?";
try{
DriverManager.registerDriver(new org.apache.derby.jdbc.EmbeddedDriver());
con = DriverManager.getConnection(url);
sql = con.prepareStatement(ssql, Statement.RETURN_GENERATED_KEYS);
sql.setString(1, cbox_chooseUser.getSelectedItem().toString());
sql.executeQuery();
ResultSet rs = sql.getGeneratedKeys();
try{
while (rs.next()) {
if(rs.getString("PW").toCharArray().equals(txt_password.getPassword())){
sql.close();
con.close();
return true;
}
} catch (NPE ...) {...}
}
I tried it multiple times wit a test user with both the pw and the username set to "test"; but I always get the same error.
Why is the recordset always Null?
Thanks for your help :)

The documentation says
ResultSet getGeneratedKeys() throws SQLException
Retrieves any auto-generated keys created as a result of executing this Statement
object.
If this Statement object did not generate any keys, an empty
ResultSet object is returned.
Your select statement isn't generating any keys that's why it's returning an empty ResultSet. You aren't inserting anything hence no keys are being generated.
You can try ResultSet rs = sql.executeQuery();. It should work.

You are using it in wrong way.
The generated keys concept should be used only in the case DML of insert type query but not in the case of select query.
select simply select the rows from the table. In this case there is no chance of any keys getting generated.
In the case of insert query if any column is configured as auto increment or kind of functionality then some keys will get generated. These keys can be caught using Statement.RETURN_GENERATED_KEYS in java.
As you are using select query there is no need of using Statement.RETURN_GENERATED_KEYS.
You just modify below lines and everything will be fine.
sql = con.prepareStatement(ssql, Statement.RETURN_GENERATED_KEYS);
sql.setString(1, cbox_chooseUser.getSelectedItem().toString());
sql.executeQuery();
ResultSet rs = sql.getGeneratedKeys();
with
sql = con.prepareStatement( ssql );
sql.setString( 1, cbox_chooseUser.getSelectedItem().toString() );
ResultSet rs = sql.executeQuery();

How to get all the rows affected by a UPDATE query in JDBC?

I have an assignment where I need to update records using a PreparedStatement. Once the record have been updated as we know update query return count, i.e., number of row affected.
However, instead of the count I want the rows that were affected by update query in response, or at least a list of id values for the rows that were affected.
This my update query.
UPDATE User_Information uInfo SET address = uInfo.contact_number || uInfo.address where uInfo.user_id between ? AND ?;
Normally it will return count of row affected but in my case query should return the ids of row or all the row affected.
I have used the returning function of PostgreSQL it is working but is not useful for me in that case.

i have used returning function of PostgreSQL but is not useful for me
It should be. Perhaps you were just using it wrong. This code works for me:
sql = "UPDATE table1 SET customer = customer || 'X' WHERE customer LIKE 'ba%' RETURNING id";
try (PreparedStatement s = conn.prepareStatement(sql)) {
s.execute(); // perform the UPDATE
try (ResultSet rs = s.getResultSet()) {
// loop through rows from the RETURNING clause
while (rs.next()) {
System.out.println(rs.getInt("id")); // print the "id" value of the updated row
}
}
}
The documentation indicates that we can also use RETURNING * if we want the ResultSet to include the entire updated row.
Update:
As #CraigRinger suggests in his comment, the PostgreSQL JDBC driver does actually support .getGeneratedKeys() for UPDATE statements too, so this code worked for me as well:
sql = "UPDATE table1 SET customer = customer || 'X' WHERE customer LIKE 'ba%'";
try (PreparedStatement s = conn.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS)) {
s.execute(); // perform the UPDATE
try (ResultSet rs = s.getGeneratedKeys()) {
while (rs.next()) {
System.out.println(rs.getInt(1)); // print the "id" value of the updated row
}
}
}
Thanks, Craig!

You might be able to use JDBC's support for getting generated keys. See the Connection.prepareStatement(String sql, int[] columnIndexes) API method, then use Statement.getGeneratedKeys() to access the results.
The spec says "the driver will ignore the array if the SQL statement is not an INSERT statement" but I think PostgreSQL's JDBC driver will actually honour your request with other statement types too.
e.g.
PreparedStatement s = conn.prepareStatement(sql, new String[] {'id'})
s.executeUpdate();
ResultSet rs = s.getGeneratedKeys();
Otherwise, use RETURNING, as Gord Thompson describes.

There are two way of doing it
1. by passing an array of column name or index of column prepareStatement
i.e conn.prepareStatement(sql, new String[] {'id','uname'})
and
2. by using Statement.RETURN_GENERATED_KEYS in prepareStatement.
My code is for this i.e as per my requirement i have developed my code you can have a look for better idea.
private static final String UPDATE_USER_QUERY= "UPDATE User_Information uInfo SET address = uInfo.contact_number || uInfo.address where uInfo.user_id between ? AND ?;";
//pst = connection.prepareStatement(UPDATE_USER_QUERY,columnNames);
pst = connection.prepareStatement(UPDATE_USER_QUERY,Statement.RETURN_GENERATED_KEYS);
ResultSet rst = pst.getGeneratedKeys();
List<UserInformation> userInformationList = new ArrayList<UserInformation>();
UserInformation userInformation;
while (rst.next()){
userInformation = new UserInformation();
userInformation.setUserId(rst.getLong("user_id"));
userInformation.setUserName(rst.getString("user_name"));
userInformation.setUserLName(rst.getString("user_lName"));
userInformation.setAddress(rst.getString("address"));
userInformation.setContactNumber(rst.getLong("contact_number"));
userInformationList.add(userInformation);
}
That think i need to achieve in this case.
Hope so this will help you a lot.

Getting null value in the foreign key field of my table in Mysql

I have 2 tables in my application:
1.newuser
2.introducer_table
Newuser1 table contains *sid**(primary key,auto-generated field)****, fathername,gender,datebirth,occupation,addharnumber as columns
1.I’m inserting values into the newuser table using java prepared statement like below:
PreparedStatement pst = con.prepareStatement("insert into newuser1 (name,fathername,gender,datebirth,occupation,aadharNumber) values(?,?,?,?,?,?)");
//pst.setString(1,NULL);
pst.setString(1,”xyz”);
pst.setString(2,"ram");
pst.setString(3,"male");
pst.setString(4,"oct25");
pst.setString(5,"emps");
pst.setString(6,"4564");
data is inserted successfully,but I want the sid value of newuser1 in my introducer_table so I write the query like this in prepared statement to select the last insert id.
My introducer_table contains the columns:
**sid(foreign key),name,accountno,sign**
PreparedStatement pst = con.prepareStatement("insert into introducer_table(sid,name,accountno,sign) values((SELECT LAST_INSERT_ID() from dual),?,?,?)");
//nomine details into data base
//pst.setString(1,NULL);
pst.setString(1,"ram");
pst.setString(2,"8945");
pst.setString(3,"ssss");
When I execute this,Im getting ‘0’ value in the sid column of introducer_table.I make sid column as not null while creating intoducer_table,even im getting the ‘zero’ value like this:
Introducer_table:
**Sid** name accountno sign
**0** ram 8945 ssss
Please help me I was stucked by this problem from so many days.

Rather than doing it your way think about using
con.prepareStatement(query, Statement.RETURN_GENERATED_KEYS);
and then after your insert
pst.executeUpdate();
ResultSet rs = prest.getGeneratedKeys();
　　
int last_inserted_id = -1;
if(rs.next())
{
last_inserted_id = rs.getInt(1);
}

Retrieving serial id from batch inserted rows in postgresql

Here is the code that works:
Connection c = ds.getConnection();
c.setAutoCommit(false);
PreparedStatement stmt = c.prepareStatement("INSERT INTO items (name, description) VALUES(?, ?)");
while (!(items = bus.take()).isEmpty()) {
for (Item item : items) {
stmt.setString(1, item.name);
stmt.setString(2, item.description);
stmt.addBatch();
}
stmt.executeBatch();
c.commit();
}
But now I need to populate another table where id is a foreign key.
If I use INSERT with RETURNING id then executeBatch fails with "A result was returned when none was expected" error.
I see several ways to solve this
Do individual insert rather than the batch insert.
Replace serial id with client generated guid.
Use some kind of a stored procedure to perform the batch insert and return a list of ids.
Of the three methods that I see the last one seems to preserve both the efficiency of batch insert and return the ids, but it is also the most complex for me as I have never written stored procedures.
Is there a better way to batch insert and get the IDs? I have no problem using postgresql specific API rather than jdbc.
If not, could any one sketch such a stored procedure?
Here is the table schema:
CREATE UNLOGGED TABLE items
(
id serial,
name character varying(1000),
description character varying(10000)
)
WITH (
OIDS=FALSE
);

Something like this should work:
// tell the driver you want the generated keys
stmt = c.prepareStatement("INSERT ... ", Statement.RETURN_GENERATED_KEYS);
stmt.executeBatch();
// now retrieve the generated keys
ResultSet rs = stmt.getGeneratedKeys();
while (rs.next()) {
int id = rs.getInt(1);
.. save the id somewhere or update the items list
}
I think (I am not sure!) that the keys are returned in the order they were generated. So the first row from the ResultSet should map to the first "item" from the list you are processing. But do verify that!
Edit
If that doesn't work, try specifying the actual columns for which the values are generated:
stmt = c.prepareStatement("INSERT ... ", new String[] {"id"});