如何使用java在sql中的datetime列中插入null值

Question

Does anyone know how to set a null value into a datetime column in a database in sql? I tried setting the String as null: String date = null; but i would get this error:

java.sql.SQLException: [Microsoft][ODBC SQL Server Driver][SQL Server]Conversion failed when converting datetime from character string .

Also I tried setting my string to no value by simply declaring it (String date;). however this would just end up setting the date as January 1, 1900.

I used 3 dropdown boxes for the user of the program to choose the month, day, and year each.

DateNew newdateprocessed;
int b, c;
String d;

//First I took the values from each drop down box.
b = Date_Processed_Month_Mod.getSelectedIndex(); 
c = Date_Processed_Day_Mod.getSelectedIndex();
d = Date_Processed_Year_Mod.getSelectedItem().toString();                
newdateprocessed = new DateNew(b, c, d);

//Then I used these values in a separate function to put them all together as just one      string
public class DateNew extends Object {
String newdate;
String monthword, newdateword;
int check=0;

public DateNew (int month, int day, String year) {

    //newdate = ""+ month + "/" + day + "/" + year;

    if (month == 0 | day == 0 | year.equals("Year")) {
        newdate=null;
        check = 1;
    }

    else {

        switch (month) {
            case 1: 
                monthword="January";
                break;
            case 2:
                monthword="February";
                break;
            case 3:
                monthword="March";
                break;
            case 4:
                monthword="April";
                break;
            case 5:
                monthword="May";
                break;
            case 6:
                monthword="June";
                break;
            case 7:
                monthword="July"; 
                break;
            case 8:
                monthword="August";
                break;
            case 9:
                monthword="September";
                break;
            case 10:
                monthword="October"; 
                break;
            case 11:
                monthword="November";
                break;
            case 12:
                monthword="December";
                break;

        }

        newdateword= monthword + " " + day + ", " + year; 
        newdate = ""+ month + "/" + day + "/" + year;
    }
    check=month;



}

public String newdate() {
    return newdate;
}

public int newdatecheck(){
    return check;
}

public String newdateword(){
    return newdateword;


}

Lastly, I would give newdateprocessed.newdate() to the column in my database. It would work fine if the user would choose a date, but if they did not choose a date that I would get an error, which is why I am trying to find a way to be able to put a null value.

Answer 1

Try to call

setNull(index,java.sql.Types.DATE)

For example

String query = "UPDATE Licenses Set Date_Processed = ?";
PreparedStatement queryStatement = (PreparedStatement)connection.prepareStatement(sql);
queryStatement.setNull(1, java.sql.Types.Date);

Answer 2

Why a string? If it's a datetime column, you could try:

Date date = null;

You seem to be passing a string to your data access code, which is being stored in a datetime column, so you are relying on the DBMS to interpret the string value and convert it to a datetime. There is no way this can handle a null value, so you are going to have to change the way you are doing this to actually pass a compatible data type like a Date instance.

Answer 3

尝试使用setDate方法（并传入null）而不是setString方法。

Answer 4

i figured out what to do. the query that i used for updating my database was originally this:

String query = "UPDATE Licenses Set Date_Processed = '" + newdateprocessed.newdate() + "'";

i took out the single quotation marks in the query and changed the query to this:

String query = "UPDATE Licenses Set Date_Processed =" + newdateprocessed.newdate();

and in my code for setting the value of newdate in my DateNew function, if it was null i set it to be:

newdate = "NULL";

and if it wasn't i set it to be:

newdate = "'" + month + "/" + day + "/" + year + "'";