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Truncated incorrect DOUBLE value using DELETE statement

int d1;
String attribute = comboBox1.getSelectedItem().toString(); // a combo box
System.out.println(attribute);
String data = t.getText(); // a textfield
System.out.println(data);
if (attribute.equals("COURSE_ID")) {
IsNumber in = new IsNumber();
d1 = in.stringToInt(data);
try {
Connection connection = DriverManager.getConnection(url, username, password);
System.out.println("connection success!!");
String sql = "DELETE FROM course WHERE ? = ?";
PreparedStatement statement = connection.prepareStatement(sql);
statement.setString(1, attribute);
statement.setInt(2, d1);
boolean rows = statement.execute();
if (rows == true) {
new ViewDatabase(user, name, pswrd);
System.out.println("COURSE_ID UNIT UPDATE SUCCESSFUL!");
frame.setVisible(false);
} else if (rows == false) {
JOptionPane.showMessageDialog(null, "Cannot find row!",
"ERROR", JOptionPane.ERROR_MESSAGE);
}
statement.close();
connection.close();
} catch (SQLException e) {
System.out.println("& i oop");
e.printStackTrace();
}
For this piece of code, whenever I try to run it, it returns "Data truncation: Truncated incorrect DOUBLE value: 'COURSE_ID'". I'm not sure what this is referring to and I searched and found some people saying that this error message is misleading, though I only found answers to selects, inserts, and updates, but not deletes.
I also turned off strict mode in MySQL, as advised from the internet, but to no avail.

You can't bind strings to actual column names in a prepared statement. So, the attribute column names must be hard-coded. One pattern which might work would be:
String sql = "";
if ("COL1".equals(attribute)) {
sql = "DELETE FROM course WHERE COL1 = ?";
}
else if ("COL2".equals(attribute)) {
sql = "DELETE FROM course WHERE COL2 = ?";
}
else {
sql = "DELETE FROM course WHERE COL3 = ?";
}
PreparedStatement statement = connection.prepareStatement(sql);
statement.setInt(1, d1);
boolean rows = statement.execute();

Where should ? be placed in a PreparedStatement? [duplicate]

This question already has an answer here:
Having a Column name as Input Parameter of a PreparedStatement
(1 answer)
Closed 7 years ago.
I am using PreparedStatement to select records from a table:
public static String getMemberInfo(String columnName, Integer memberId) {
String memberInfo = "";
String sql = "SELECT ? FROM member WHERE member_id = ?";
DatabaseConnector.setConn();
try(Connection conn = DatabaseConnector.getConn();
PreparedStatement ps = conn.prepareStatement(sql)) {
ps.setString(1, columnName);
ps.setInt(2, memberId);
try(ResultSet rs = ps.executeQuery()) {
if(rs.next()) {
memberInfo = rs.getString(columnName);
}
}
} catch(SQLException se) {
se.printStackTrace();
}
return memberInfo;
}
When I use
SELECT " + columnName + " FROM member WHERE member_id = ?, it works.
But when I use
SELECT ? FROM member WHERE member_id = ?, it does not.
Where should ? be placed in prepared statements?

? is for input values (typically in the WHERE clause conditions).
? is not for selected columns.

Column name must be hard-coded, Only column values can be set using ?.
but you can set dynamic column name by doing something like this :
String sql = "SELECT "+ columnName +" FROM member WHERE member_id = ?";

Data writing error

I'm inserting some data into a mySql database. For some unknown reason the data is not being inserted into my table. This worked fine with SQLITE.
Here is my code:
try {
Class.forName("com.mysql.jdbc.Driver");
Connection conn = DriverManager.getConnection(url, username, password);
String query1 = "insert into Project (uniqueid,name,address,startingdate,estcompletion,engname) values(?,?,?,?,?,?)";
String query2 = "insert into EngineerData (UniqueId,Name,Password) values(?,?,?)";
String query3 = "insert into " +tableName +" (UniqueId,Category,Item,EstimatedQuantity,Unit,UnitPrice,TotalPrice,TotalSpent) values(?,?,?,?,?,?,?,?)";
String query4 = "insert into ProjectImages (uniqueId, Path) values(?,?)";
PreparedStatement pst1= conn.prepareStatement(query1);
PreparedStatement pst2 = conn.prepareStatement(query2);
PreparedStatement pst3 = conn.prepareStatement(query3);
PreparedStatement pst4 = conn.prepareStatement(query4);
pst1.setInt(1, uniqueID);
pst1.setString(2, projectName.getText());
pst1.setString(3, address.getText());
pst1.setString(4, day1.getText()+"/"+month1.getText()+"/"+year1.getText());
pst1.setString(5, day2.getText()+"/"+month2.getText()+"/"+year2.getText());
pst1.setString(6, engineerName.getText());
pst2.setInt(1, uniqueID);
pst2.setString(2, engineerName.getText());
pst2.setString(3, engineerPassword.getText());
try{
for (int j = 0; j < table.getRowCount(); j++ ){
pst3.setInt(1, uniqueID);
pst3.setString(2, table.getValueAt(j, 0).toString());
pst3.setString(3, table.getValueAt(j, 1).toString());
pst3.setString(4, table.getValueAt(j, 2).toString());
pst3.setString(5, table.getValueAt(j, 3).toString());
pst3.setString(6, table.getValueAt(j, 4).toString());
pst3.setString(7, table.getValueAt(j, 5).toString());
pst3.setDouble(8, 0.0);
pst3.execute();
}}catch(Exception e3){
/*JOptionPane.showMessageDialog(null, e3);
*
*/
}
pst4.setInt(1, uniqueID);
pst4.setString(2, null);
pst1.execute();
pst2.execute();
pst4.execute();
System.out.println(pst1.toString());
System.out.println(pst2.toString());
pst1.close();
pst2.close();
pst3.close();
pst4.close();
conn.close();
}

You should leave out auto generated column "uniqueID" and rewrite your code.
Ex.
String query4 = "insert into ProjectImages (Path) values(?)";
Another approach - passing null value for auto generated column. Ex.
String query4 = "insert into ProjectImages (uniqueId, Path) values(null,?)";

Without the stack trace it might be difficult to get where this is not working. It might be a INDEX constraint exception, a null pointer exception, ... But, I'd suggest to format differently the date, instead of
day1.getText()+"/"+month1.getText()+"/"+year1.getText()
I'd use
year1.getText()+"-"+month1.getText()+"-"+day1.getText()
(check the MySQL documentation and especially the STR_TO_DATE() function, but you probably don't need it).
And also there's room to improve your code (following Rajesh's comment):
While probably you're using Java 7 or above, I'd add the try-with statement for the connection;
Catching Exception is generally bad practice, I'd go for a fine-grain try-catch with SQLException, ...
I can't see any transaction strategy in place. I'd be worried while some of the pst?.execute() works fine and another doesn't, leaving your database in an inconsistent state.

Java mysql execute update

So I have a method that looks up a foreign key in a database. If the foreign key does not exist it will add an entry into the database. Now what I am doing from that point after inserting the new record, is re-querying again to get the foreign key. Is this overkill or is this the right way to do this? Thanks
private String getTestType(TestResult testResult) {
String testTypeId = "";
String query = String.format("SELECT id FROM test_types WHERE " +
"name='%s'", testResult.getTestType());
try {
st = con.prepareStatement(query);
rs = st.executeQuery();
if (rs.next()) {
testTypeId = rs.getString("id");
} else {
st = con.prepareStatement("INSERT INTO test_types (name, " +
"created_at) VALUES (?, ?)");
st.setString(1, testResult.getTestType());
st.setTimestamp(2, new java.sql.Timestamp(System
.currentTimeMillis()));
st.executeUpdate();
st = con.prepareStatement(query);
rs = st.executeQuery();
if (rs.next()) {
testTypeId = rs.getString("id");
}
}
} catch (SQLException e) {
e.printStackTrace();
System.out.println("There was an issue getting and or creating " +
"test Type");
}
return testTypeId;
}

Since you are inserting a new row into DB, you have to do a query to get back the auto increment field(id). Currently they way you are doing is workable. But there are few alternatives in query:
Obtaining the id using last_insert_id():
rs = st.executeQuery("select last_insert_id() as last_id");
id= rs.getString("last_id");
Another approach can be doing the MAX over the id column of the table.
I believe these are will be much faster than your query as you are doing string comparison in where clause.

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;