I have created a table named student including column stu_id, stu_name & Blood_group.I created a delete button to delete rows and I used the following code when delete button is pressed.I take input using jtextfield.But this can only delete by taking input in stu_id.But now i also want to delete by Blood_group or stu_name or both.here is my code.

private void cmd_deleteActionPerformed(java.awt.event.ActionEvent evt) {                                           

int p= JOptionPane.showConfirmDialog(null,"Do you really want to      delete?","Delete",JOptionPane.YES_NO_OPTION);
if(p==0){
try{


String sql="Delete from student where stu_id=?";



pst=conn.prepareStatement(sql);
pst.setString(1, jTextField1.getText());

pst.execute();

}       
catch(Exception e){
 JOptionPane.showMessageDialog(null, e);
 }
   Update_table();
}                                          

}

I figured i have to change my query.So i changed my code to this.

 private void cmd_deleteActionPerformed(java.awt.event.ActionEvent evt) {                                           

int p= JOptionPane.showConfirmDialog(null,"Do you really want to delete?","Delete",JOptionPane.YES_NO_OPTION);
if(p==0){
    try{

  String s[]=new String[20];
s[1]=jTextField1.getText();
s[2]=jTextField2.getText();
s[3]=jTextField3.getText();

String sql="Delete from student where ";

if(s[1] != null)
    sql=sql+"stu_id='"+s[1]+"' AND ";

if(s[2] != null)
    sql=sql+"stu_name='"+s[2]+"' AND ";

if(s[3]!= null)
    sql=sql+"Blood_group='"+s[3]+"'";



pst=conn.prepareStatement(sql);

pst.execute();

}       
catch(Exception e){
 JOptionPane.showMessageDialog(null, e);
 }
   Update_table();
}                                          

}

But this didn't work.Unfortunately now i have to give input all 3 column to delete a row.How can i solve that?Did my ques was clear.Thanx in advance.

Recommended Answers

Maybe OR those conditions rather than ANDing them?

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Then you will have to construct different SQL commands for each of the 6 possible combinations of criteria.

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This isn't a Java question, it's an SQL question, and I'm not the best person to answer it. Try asking how to phrase the SQL query in our Databases forum - someone will know the answer.

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The text from an empty field is "" - a string of zero length.
You can't test the contents of a string with = or ==, you need equals(...).
The safest test here is to trim off any blank chars and see if anything is left, ie
s[1].trim().length() == 0

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All 13 Replies

Maybe OR those conditions rather than ANDing them?

It won't work.For example i want to delete the row which contain stu_name=mark AND blood_group=B+.If i use OR than it will delete all row containing B+ and also all row containing mark.any other solution please.

Then you will have to construct different SQL commands for each of the 6 possible combinations of criteria.

But if i have 10 column instead of 3 column than i think i won't be the best idea to combine the possible criteria.Please give me a better solution.

This isn't a Java question, it's an SQL question, and I'm not the best person to answer it. Try asking how to phrase the SQL query in our Databases forum - someone will know the answer.

Thankyou.Your help mean a lot to me

Can you tell me what is the default value of a jtextfield.I added those jtextefield by drag and drop process in netbeans.Than i right click on it,click edit text and than i deleted the text(it was 'jtextfield').Now what is the value of jtextfield? Is it "" or null or anything else?

By "value" do you mean the text in the JTextField? If so, the default is a zero-length String, ""

Than i think it should work the way i did in the second code by typing s[1/2/3]="" instead of s[1/2/3]=null. But it didn't work.Can you tell me why?

I have no idea what you are trying to achieve without any context. And "didn't weork" tells me nothing.
s is an array of Strings which was populated from the text of some JTextFields. Did you want to change the text fields? If so you need to use JTextField's setText method

I have done that already.I tried both null and "".But it didn't work.I changed the code to this.I used set text method before the new code.

if (s[1] != null || s[2] != null || s[3] != null)
{
String sql="Delete from student where ";
String andsql="";
if(s[1] != null)
{
sql=sql+"stu_id='"+s[1]+"' ";
andsql=" and ";
}
if(s[2] != null )
{
sql=sql+andsql+"stu_name='"+s[2]+"' ";
andsql=" and ";
}
if(s[3]!= null)
{
sql=sql+andsql+"Blood_group='"+s[3]+"'";
}
pst=conn.prepareStatement(sql);
pst.execute();
}

But I found the mistake.I printed the String "sql" inside the if condition just before "pst=conn.prepareStatement(sql);" of this code.I have given no input in the jtextfield and pressed the delete button.Than the output appears in output screen is
Delete from student where stu_id='' and stu_name='' and Blood_group=''
So the initial value is not null.I tried "" instead of null.But it reamain the same.What is the initial value?

The text from an empty field is "" - a string of zero length.
You can't test the contents of a string with = or ==, you need equals(...).
The safest test here is to trim off any blank chars and see if anything is left, ie
s[1].trim().length() == 0

Thanks a lot.At last my problem is solved.Jamescherill, you again became my life saver.

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