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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.

Java: SQL Query: rs.next() is false after updating a column

I have a strange problem. I have a database and I want to change the values of a column. The values are safed in an Arraylist (timelist).
In order to write the values in the right row, I have a second Arrylist (namelist). So I want to read the first row in my Database, than I check the namelist and find the name. Than i take the matching value out of the timelist and write it into the database into the column "follows_date" in the row, matching to the name.
And than I read the next row of the Database, until there are no more entries.
So the strange thing is, if I change nothing in the database, the while(rs.next()) part works.
For example:
ResultSet rs = statement.executeQuery("SELECT username FROM users");
while(rs.next()){
// read the result set
String name = rs.getString("username");
System.out.println("username = " + name); //liest die namen
}
}
This would print me every name after name. But when I change the table, the while loop ends after that. (no error, the program just finishes)
ResultSet rs = statement.executeQuery("SELECT username FROM users");
while(rs.next()){
// read the result set
String name = rs.getString("username");
System.out.println("username = " + name); //writes the name
//look, if name is in Arraylist "namelist"). if yes, than write the matching date from "timelist" into the database.
if (namelist.contains(name)){
System.out.println("name found: "+ name);
int listIndizi = namelist.indexOf(name); //get index
Long indiziDatum = (long) timelist.get(listIndizi); //get date from same Index
System.out.println(indiziDatum); // print date so i can see it is correct (which it is)
statement.executeUpdate("UPDATE users SET follows_date ="+ indiziDatum +" WHERE username = '"+name+"'"); //updates the follows_date column
}
}
Everything works fine, except that now, the while loop doesn't continues after the first passage, but ends.

The resultSet of a statement is closed and will not return further results if you execute another statement. Create a new separate statement object for the update and everything should work as excepted.
Statement statement1 = connection.createStatement();
Statement statement2 = connection.createStatement();
ResultSet resultSet1 = statement1.executeQuery("SELECT username FROM users");
while(resultSet1.next()){
...
statement2.executeUpdate("UPDATE users ..."));
}

As to Why it happens:
Here is the explanation from the official documentation:
A ResultSet object is automatically closed when the Statement object that generated it is closed, re-executed, or used to retrieve the next result from a sequence of multiple results.
Alternative Approach:
From your sample, it seems you are trying to update the "same" row in your resultSet, you should consider using an Updatable ResultSet.
Sample code from the official documentation:
public void modifyPrices(float percentage) throws SQLException {
Statement stmt = null;
try {
stmt = con.createStatement();
stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_UPDATABLE);
ResultSet uprs = stmt.executeQuery(
"SELECT * FROM " + dbName + ".COFFEES");
while (uprs.next()) {
float f = uprs.getFloat("PRICE");
uprs.updateFloat( "PRICE", f * percentage);
uprs.updateRow();
}
} catch (SQLException e ) {
JDBCTutorialUtilities.printSQLException(e);
} finally {
if (stmt != null) { stmt.close(); }
}
}

Getting next value from sequence

I have a bit of code here to get the next value of my sequence, but it is adding the total number of records onto the result each time.
I'm only learning about prepared Statements, I'm thinking this is something small, maybe rset.next() should be something else?
public void add( String title, String actor, String genre ) {
try {
String sql2 = "Select movie_seq.nextval from Movie";
pstmt = conn.prepareStatement(sql2);
rset = pstmt.executeQuery();
int nextVal = 0;
if(rset.next())
nextVal = rset.getInt(1);
String queryString = "Select MovieID, Title, Actor, Genre from Movie";
pstmt = conn
.prepareStatement(queryString,
ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_UPDATABLE);
rset = pstmt.executeQuery();
rset.moveToInsertRow();
rset.updateInt(1, nextVal);
rset.updateString(2, title);
rset.updateString(3, actor);
rset.updateString(4, genre);
rset.insertRow();
pstmt.executeUpdate();
} catch (SQLException e2) {
System.out.println("Error going to previous row");
System.exit(1);
}
}
Any help appreciated.

I think you don't need the call to pstmt.executeUpdate();
As stated in ResultSet doc, the function insertRow stores the row in the Dataset AND in the database.
The following code shows all that's necessary to add a new row:
rset.moveToInsertRow(); // moves cursor to the insert row
rset.updateString(1, "AINSWORTH"); // updates the
// first column of the insert row to be AINSWORTH
rset.updateInt(2,35); // updates the second column to be 35
rset.updateBoolean(3, true); // updates the third column to true
rset.insertRow();
rset.moveToCurrentRow();

Why dont you iterate using while rather than if . something like this
List lst = new ArrayList();
Someclass sc = new SomeClass(); //object of the class
String query = "SELECT * from SomeTable";
PreparedStatement pstmt = sqlConn.prepareStatement(query);
ResultSet rs = pstmt.executeQuery();
Role role = null;
while (rs.next()) {
String one = rs.getString(1);
String two = rs.getString(2);
boolean three = rs.getBoolean(3);
//if you have setters getters for them
sc.setOne(one);
sc.setTwo(two);
sc,setThree(three);
lst.add(sc)
}
//in the end return lst which is of type List<SomeClass>
}

Shouldn't you be doing this instead?:
String sql2 = "Select " + movie_seq.nextval + " from Movie";
As it is, it seems like you're passing a slightly bogus string into the SQL query, which is probably defaulting to the max index (not 100% positive on that). Then rs.next() is just incrementing that.

SQL command from eclipse using JDBC

I have been searching and trying different stuff for awhile, but have not found an answer. I'm trying to make a connection to sql using JDBC from eclipse. I am having trouble when I need to select a string in the database. If I use:
Select name from data where title = 'mr';
That works with terminal/command line but when I try to use eclipse where I use
statement sp = connection.createstatement();
resultset rs = sp.executequery("select name from data where title = '" + "mr" + "'");
It does not give me anything while the terminal input does. What did I do wrong in the eclipse? Thanks
Heres a part of the code. Sorry, its a bit messy, been trying different things.
private boolean loginChecker(String cid, String password) throws SQLException{
boolean check = false;
PreparedStatement pstatment = null;
Statement stmt = null;
//String query = "SELECT 'cat' FROM customer";
String query = "select '"+cid+"' from customer where password = '"+password+"'";
try {
System.out.println("in try......");
//stmt = con.createStatement();
//ResultSet rs = stmt.executeQuery(query);
PreparedStatement prepStmt = con.prepareStatement(query);
ResultSet rs = prepStmt.executeQuery();
//System.out.print(rs.getString("cid"));
while(rs.next()){
check = true;
System.out.print(rs.getString("cid"));
}
} catch (SQLException e ) {
e.printStackTrace();
} finally {
if (stmt != null) {
//stmt.close();
}
}
return check;
}
Second try on a simpler query:
public List<Object> showTable() {
List<Object> result = new ArrayList<Object>();
String name = "bob";
try
{
PreparedStatement preStatement = con.prepareStatement("select total from test where name = ?");
preStatement.setString(1, name);
ResultSet rs1 = preStatement.executeQuery();
while(rs1.next()){
System.out.println("there");
System.out.println(rs1.getInt("total"));
}
}
catch (SQLException ex)
{
System.out.print("Message: " + ex.getMessage());
}
return result;
}

Remove the quotes around the column name.
String query = "select "+cid+" from customer where password = '"+password+"'";
You've not mentioned which database you're working with but many databases like Oracle change the column case to upper case unless they're quoted. So, you only quote table columns if that's how you had created them. For example, if you had created a table like
CREATE TABLE some_table ( 'DoNotChangeToUpperCase' VARCHAR2 );
Then you would have to select the column with quotes as well
SELECT 'DoNotChangeToUpperCase' FROM some_table
But, if you didn't create the table using quotes you shouldn't be using them with your SELECTs either.

Make sure you are not closing the ResultSet before you are trying to use it. This can happen when you return a ResultSet and try to use it elsewhere. If you want to return the data like this, use CachedRowSet:
CachedRowSet crs = new CachedRowSetImpl();
crs.populate(ResultSet);
CachedRowSet is "special in that it can operate without being connected to its data source, that is, it is a disconnected RowSet object"
Edit: Saw you posted code so I thought I add some thoughts. If that is your ACTUAL code than the reason you are not getting anything is because the query is probably not returning anything.
String query = "select '"+cid+"' from customer where password = '"+password+"'";
This is wrong, for two reasons. 1) If you are using prepared statements you should replace all input with '?' so it should look like the following:
String query = "select name from customer where password = ?";
Then:
PreparedStatement prepStmt = con.prepareStatement(query);
prepStmt.setString(1, password);
ResultSet rs = prepStmt.executeQuery();
2)
System.out.print(rs.getString("cid"));
Here are are trying to get the column named "cid", when it should be the name stored in cid. You should actually never be letting the user decide what columns to get, this should be hardcoded in.

How to check if a record with a specific primary key exists in a MySql table from JDBC

How can i find out, from a Java program using JDBC if my table has a record with a specific primary key value? Can i use the ResultSet somehow after i issue a SELECT statement?

Count might be a better idea for this case. You can use it like so:
public static int countRows(Connection conn, String tableName) throws SQLException {
// select the number of rows in the table
Statement stmt = null;
ResultSet rs = null;
int rowCount = -1;
try {
stmt = conn.createStatement();
rs = stmt.executeQuery("SELECT COUNT(*) FROM " + tableName + " WHERE.... ");
// get the number of rows from the result set
rs.next();
rowCount = rs.getInt(1);
} finally {
rs.close();
stmt.close();
}
return rowCount;
}
Taken from here.

You can do something like
private boolean hasRecord(String id) throws SQLException {
String sql = "Select 1 from MyTable where id = ?";
PreparedStatement ps = dbConn.prepareStatement(sql);
ps.setString(1,id);
ResultSet rs = ps.executeQuery();
return rs.next();
}

You can do that in four steps.
Write SQL. Something like select count(1) from table where column = 34343 will do.
Learn how to get connection using JDBC.
Learn about PreparedStatements in Java.
Learn how to read values from ResultSet.

select case
when exists (select 1
from table
where column_ = '<value>' and rownum=1)
then 'Y'
else 'N'
end as rec_exists
from dual;