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How to convert prepared statement into String [duplicate]

This question already has answers here:
Get value from a ResultSet by name
(2 answers)
Closed 1 year ago.
I am trying to set a string value into DB using prepared statement and Result Set. But it inserts into DB row this "com.mysql.cj.jdbc.result.ResultSetImpl#fcd6521"
PreparedStatement check = connection.prepareStatement(
"SELECT buildingName FROM building GROUP BY buildingId HAVING buildingId = ?");
check.setInt(1, building_id);
ResultSet rs = check.executeQuery();
insert.setString(1, String.valueOf(rs));
insert.executeUpdate();

I think that you need to read the tutorial indicated by #user16320675
A ResultSet is a type of set. It has to be accessed like that:
//if you expects receive only one buildName you use a simple if, otherwise you have to use a loop and a list or something like that
String text;
if(rs.next()){
text = rs.getString(0);
}
//index it's related to buildingName

java.sql.SQLException: Closed Resultset: next [duplicate]

This question already has an answer here:
SQLException: the result set is closed
(1 answer)
Closed 3 years ago.
I didn't find the reason for a SQLExeption, I got it at while(dbrs.next()). It is simple, it was working, but after update to Oracle Server 19, I got this error. I got still a result set in Oracle Developer with the same account.
Statement st = conn.createStatement();
if (Oracle){
ResultSet dbrs = st.executeQuery("select table_name from all_tables");
while(dbrs.next()){
if (dbrs.getString(1).equals(G_IN)){
st.execute("DROP TABLE "+G_IN);
System.out.println(G_IN+" gelöscht");
}
}
dbrs.close();
}else{
String loeschen="DROP TABLE IF EXISTS \"" + G_IN +"\"";
System.out.println(loeschen);
st.execute( loeschen );
}

You shouldn't reuse a Statement object as is the case in your while loop. To execute a new query, you need to use a new Statement object.
Replace
st.execute("DROP TABLE "+G_IN);
with
conn.createStatement().execute("DROP TABLE "+G_IN);
and it should work.

Placeholders not working when using SQL statement in Java (JDBC) [duplicate]

This question already has answers here:
Variable column names using prepared statements
(7 answers)
Using Prepared Statements to set Table Name
(8 answers)
Closed 4 years ago.
Very first question here so I apologize for any mistakes and imperfections.
Basically there are three files, my main method tech_supportv1, login_controller containing a class used to store a bunch of methods, and login.java, a javabean.
The point is to check if a certain row exists on the tech_support database. To do so I'm trying to use the code below. (db_util and type are classes containing connection data, they are tested and they work).
ISSUE: the data from the main method seems not be pasted into the string in the appropriate placeholders, and an error is returned. (Of course if I manually enter the strings instead of using placeholders, everything works just fine.)
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ''technicians' WHERE 'techID' LIKE 16' at line 1
I tired to look at the mariaDB docs but all the other syntax provided yields the same results.
So this the main method.
public class Tech_support_v1 {
public static void main(String[] args) {
System.out.println("Start.");
login bean = new login();
bean.setTable("technicians");
bean.setColumn("techID");
bean.setID(16);
login_controller.select(bean);
}
}
This is the select method (with bean as argument, login is the Javabean class).
public static boolean select(login bean) {
String sql = "SELECT * FROM ? WHERE ? LIKE ?";
ResultSet rs;
try (
Connection conn = db_util.getConn(db_type.MYSQL);
PreparedStatement stmt = conn.prepareStatement(sql);
) {
stmt.setString(1, bean.getTable());
stmt.setString(2, bean.getColumn());
stmt.setInt(3, bean.getID());
rs = stmt.executeQuery();
if (rs.next()) {
System.out.println("Y");
return true;
} else {
System.err.println("N");
return false;
}
} catch (Exception e) {
System.err.println(e);
return false;
}
}
I won't include the bean class because it's literally only three variables with the relative set/get methods. Also the database runs with MariaDB, and is MySQL.
Thanks to everyone in advance.

You have multiple problems with your code :-)
First, you can't set table or column names with "setString" in a Prepared Statement!
See this Question: How to use a tablename variable for a java prepared statement insert
Second, as Daniel Pereira pointed out: You are trying to use a "like" Statement with "setInt"! See: https://dev.mysql.com/doc/refman/8.0/en/pattern-matching.html

You are comparing with LIKE but you are setting an Int. Change the LIKE to = and see if it works.

Try doing something like this:
String sql="SELECT * FROM :table ";
try (
Connection conn = db_util.getConn(db_type.MYSQL);
PreparedStatement stmt = conn.prepareStatement(sql);
)
{
String query = StringUtils.replace(sql, ":table", bean.getTable());
stmt.executeQuery(query);
}

java.sql.SQLException : Operation not allowed after ResultSet closed [duplicate]

This question already has answers here:
Getting java.sql.SQLException: Operation not allowed after ResultSet closed
(2 answers)
Closed 4 years ago.
Can anyone point me in the write direction to solve the error: SQLException: Operation not allowed after ResultSet closed
Here is the code i believe the error occurs in
Statement stmt = con.createStatement();
String query1 = "";
String query2 = "";
int candidateNo = 42;
query1 = "SELECT * FROM Candidates WHERE CandidateNo = "+ candidateNo;
ResultSet rs = stmt.executeQuery(query1);
//If query can be completed then display name and prompt to continue
if(rs.next()){
query2 = "SELECT * FROM Achieved WHERE CandidateNo = " + candidateNo;
ResultSet ts = stmt.executeQuery(query2);
}
I have tried using resultset rs = null; to create the variable but the error still occurs

You are iterating over the ResultSet bound to a Statement , then while iterating, you are using the exact same Statement object to issue a new query and get and iterate over another ResultSet .
This won't work as long as you are not done with the processing of the first ResultSet, so consider using a distinct Statement object for your second query .

In your code you used 2 ResultSet executing the same Statement object (stmt)concurrently. Use different Statement Objects for both queries.

why we use next() method in java? [duplicate]

This question already has answers here:
What does "if (rs.next())" mean?
(7 answers)
Closed 6 years ago.
Here is the code
Class.forName("net.ucanaccess.jdbc.UcanaccessDriver");
Connection conn=DriverManager.getConnection("jdbc:ucanaccess://C:\\Users\\MUHAMMAD SHAHAB\\STUD1.accdb");
Statement st = conn.createStatement();
String sql="select Username,Password from SUN where Username='"+user+"'and Password='"+pass+"'";
ResultSet rs=st.executeQuery(sql);
int count=0;
while(rs.next()) {
count=count+1;
}
if(count>0) {
JOptionPane.showMessageDialog(null, "Access granted");
} else if(count<1) {
JOptionPane.showMessageDialog(null,"User Not Found\nAccess is Denied");
}
I am creating a user verification system in Java and I have connected my program with MS Access. I have inserted some records in the fields of table SUN in MS Access and it is working properly. But I just want to know the working of next() method and count variable in my program.

It moves (or tries to, returning a boolean telling whether it succeeded or not) the resultset cursor forward. The count variable is useless, since you can just write if(rs.next()) to determine which message is shown.