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Query that returns the column type integer for a given table

JDBC supports the following:
ResultSet columns = connection.getMetaData().getColumns(null, schema, tableName, null);
This way I can retrieve information for all columns in the given table including the DATA_TYPE information. That information is of type int in java.
I used the following query to retrieve column name and data type but this returns the string representation of data type and I need int :
select column_name, data_type from all_tab_cols where table_name = 'tablename' and owner = 'owner';
How does the line of java code translate to a query in Oracle DB ?
How can I retrieve the int representation of a column ?
I would use a join but I don't know where to get the information from. Where does Oracle store these informations ?

For running SQL against a DB without using any ORM tools like hibernate, you can take a look at PreparedStatement class.
If you want to look at the "metadata" about the columns your PreparedStatement returned, you can take a look at the getMetaData() method, documentation can be found here and then ask the ResultSetMetaData about the column type: getColumnType(<0 based index of the column you want to find the type>) documentation can be found here
Regarding your question about how Java translates to Query in Oracle, it is too broad to be described in an answer. I would recommend looking for a tutorial on JDBC or the official tutorial.

SQL Update : WHERE clause error

I don't know whats wrong with this query :
SQL = "UPDATE "+ choosenClass +" SET COUNT = "+count+" WHERE NAME = "+names;
stmt2.executeUpdate( SQL );
Error :
java.sql.SQLSyntaxErrorException: Column 'RAMAYAH' is either not in any table in the FROM list or appears within a join specification and is outside the scope of the join specification or appears in a HAVING clause and is not in the GROUP BY list. If this is a CREATE or ALTER TABLE statement then 'RAMAYAH' is not a column in the target table.
It says Column RAMAYAH is not there but the string "RAMAYAH" itself is taken from the same table. Help Please.

Try to enclose the string into single quotes:
SQL = "UPDATE "+ choosenClass +" SET COUNT = "+count+" WHERE NAME = '"+names+"'";
stmt2.executeUpdate( SQL );

Apart from SQL-Injection vulnerability as mentioned by others in comment; your query has few more mistakes/issues.
You need to quote the filter value in WHERE condition WHERE NAME = "+names should be
WHERE NAME = '"+names+"'". Otherwise, your query will be formed like below and query engine will presume that there exist a column named RAMAYAH in your table in question.
UPDATE tab1 SET COUNT = 10 WHERE NAME = RAMAYAH;
Also, in your UPDATE statement, you have a column names COUNT which is a reserve word. You need to escape it to be in safe side.
If you are using mysql then use backtique
for sql-server use [] square bracket
for postgresql and oracle use "" double-quote

Oracle & java dynamic 'Order by' clause

I am trying to build a dynamic sql query in java (shown below)
sqlStr = "Select * " +
"from " + tableName
if(tableName!=null){
if(tableName.equals("Table1"){
sqlStr = sqlStr.concat("order by city desc");
}else if(tableName.equals("Table2"){
sqlStr = sqlStr.concat("order by country desc");
}else if(tableName.equals("Table3"){
sqlStr = sqlStr.concat("order by price desc");
}
}
Now what i would like to do is to add a final 'else' statement which would order the query based on whether the table contains a column named 'custID'. There will be several tables with that column so i want to sort the ones that have that column by custID. (Rather than having hundreds of additional if statements for each table that does have that column name.) Is this possible? i have seen people using the 'decode' function but i cant work out how to use it here.

Use DatabaseMetaData to get the table information.
You can use the getTablexxx() and getColumnxx() methods to get the table information.
Connection conn = DriverManager.getConnection(.....);
DatabaseMetaData dbmd = conn.getMetaData();
dbmd.getxxxx();
Note: you forgot space in your code before ORDER BY clause.

If you are happy with hardcoding things, a way to avoid multiple conditionals would be to store a list of all the tables that include custID.
private final static String tablesWithCustID = "/TableX/TableY/TableZ/";
...
if (tablesWithCustID.contains( tableName )) {
sqlStr = sqlStr.concat("order by custID")
}
You could use a List instead of a simple delimited string if you like.
Perhaps better, you could store a map with table names as the key, and the sort string as the value. Load it up once, then you don't need any conditional at all.

The most straight-forward way to do it is to read the column definitions from USER_TAB_COLUMNS or ALL_TAB_COLUMNS and check for the existence of a custID column. Without crazy PL/SQL tricks, you won't be able to solve this in SQL alone.
BTW, there is a " " missing between tableName and the order by clauses.

I understand that you're looking for a solution that can do this in one query, i.e. without running a separate metadata query beforehand.
Unfortunately, this won't be possible. The decode function can do some dynamic things with column values, but not with column name. And you're looking for a solution dynamically derive the column name.
An alternative might be to just add ORDER BY 1, 2. This is an old syntax that means order by the first and than by the second column. It might be a good solution if the custID column is the first column. Otherwise it at least gives you some sorting.

How about ArrayList.contains()?
You can create a list of tables which have that column, and just check for tables.contains(tablename) in the final if condition.

How to invertly select columns in sql?

If I have a SQL table with columns:
NR_A, NR_B, NR_C, NR_D, R_A, R_B, R_C
and on runtime, I add columns following the column's sequence such that the next column above would be R_D followed by R_E.
My problem is I need to reset the values of columns that starts with R_ (labeled that way to indicate that it is resettable) back to 0 each time I re-run my script . NR_ columns btw are fixed, so it is simpler to just say something like:
UPDATE table set col = 0 where column name starts with 'NR_'
I know that is not a valid SQL but I think its the best way to state my problem.
Any thoughts?
EDIT: btw, I use postgres (if that would help) and java.

SQL doesn't support dynamically named columns or tables--your options are:
statically define column references
use dynamic SQL to generate & execute the query/queries
Java PreparedStatements do not insulate you from this--they have the same issue, just in Java.

Are you sure you have to add columns during normal operations? Dynamic datamodels are most of the time a realy bad idea. You will see locking and performance problems.
If you need a dynamic datamodel, take a look at key-value storage. PostgreSQL also has the extension hstore, check the contrib.

If you don't have many columns and you don't expect the schema to change, just list them explicitly.
UPDATE table SET NR_A=0;
UPDATE table SET NR_B=0;
UPDATE table SET NR_C=0;
UPDATE table SET NR_D=0;
Otherwise, a simple php script could dynamically build and execute your query:
<?php
$db = pg_connect("host=localhost port=5432 user=postgres password=mypass dbname=mydb");
if(!$db) die("Failed to connect");
$reset_cols = ["A","B","C","D"];
foreach ($col in $reset_cols) {
$sql = "UPDATE my_table SET NR_" . $col . "=0";
pg_query($db,$sql);
}
?>
You could also lookup table's columns in Postgresql by querying the information schema columns tables, but you'll likely need to write a plpgsql function to loop over the query results (one row per table column starting with "NR_").

if you rather using sql query script, you should try to get the all column based on given tablename.
maybe you could try this query to get all column based on given tablename to use in your query.
SELECT attname FROM
pg_attribute, pg_type
WHERE typname = 'tablename' --your table name
AND attrelid = typrelid
AND attname NOT IN ('cmin', 'cmax', 'ctid', 'oid', 'tableoid', 'xmin', 'xmax')
--note that this attname is sys column
the query would return all column with given tablename except system column

Variable column names using prepared statements

I was wondering if there was any way to specify returned column names using prepared statements.
I am using MySQL and Java.
When I try it:
String columnNames="d,e,f"; //Actually from the user...
String name = "some_table"; //From user...
String query = "SELECT a,b,c,? FROM " + name + " WHERE d=?";//...
stmt = conn.prepareStatement(query);
stmt.setString(1, columnNames);
stmt.setString(2, "x");
I get this type of statement (printing right before execution).
SELECT a,b,c,'d,e,f' FROM some_table WHERE d='x'
I would, however, like to see:
SELECT a,b,c,d,e,f FROM some_table WHERE d='x'
I know that I cannot do this for table names, as discussed
here, but was wondering if there was some way to do it for column names.
If there is not, then I will just have to try and make sure that I sanitize the input so it doesn't lead to SQL injection vulnerabilities.

This indicates a bad DB design. The user shouldn't need to know about the column names. Create a real DB column which holds those "column names" and store the data along it instead.
And any way, no, you cannot set column names as PreparedStatement values. You can only set column values as PreparedStatement values
If you'd like to continue in this direction, you need to sanitize the column names (to avoid SQL Injection) and concatenate/build the SQL string yourself. Quote the separate column names and use String#replace() to escape the same quote inside the column name.

Prepare a whitelist of allowed column names. Use the 'query' to look up in the whitelist to see if the column name is there. If not, reject the query.

For MySQL prepared statements with NodeJS (mysqljs/mysql), what you need to know is that ? is for values, but if you need to escape column names, table names etc, use ?? instead.
Something like this will work:
SELECT ??, ??, ?? FROM ?? WHERE ?? < ?
Set values to ['id', 'name', 'address', 'user', 'id', 100]

I think this case can't work because the whole point of the prepared statement is to prevent the user from putting in unescaped query bits - so you're always going to have the text quoted or escaped.
You'll need to sanitize this input in Java if you want to affect the query structure safely.

Use sql injection disadvantage of Statement Interface as advantage.
Ex:
st=conn.createStatement();
String columnName="name";
rs=st.executeQuery("select "+ columnName+" from ad_org ");

public void MethodName(String strFieldName1, String strFieldName2, String strTableName)
{
//Code to connect with database
String strSQLQuery=String.format("select %s, %s from %s", strFieldName, strFieldName2, strTableName);
st=conn.createStatement();
rs=st.executeQuery(strSQLQuery);
//rest code
}

Below is the solution in java.
String strSelectString = String.format("select %s, %s from %s", strFieldName, strFieldName2, strTableName);