Need help PrepareStatement

[hungleon88]

i already read somebook, search on google, and almost the code i get are:

String str = " UPDATE Demo_table SET ? = ? WHERE Name like ? ";
PrepareStatement preStm = cn.prepareStatement(str);

preStm.setString (1,"Mark");
preStm.setDouble(2,100);
preStm.setString(3,"DBSJ");


When i exactly type that code and run, it's appear 1 record updated.
But when i use query (Select * from Demo_table) in SQLServer 2005 , the record which name is "DBSJ" not updated.
Same trouble with Delete.
Only Insert work good.

please help !!! :(

[masijade]

You can only use the placeholders for values, not for tables, columns, schemas, or anything else of that sort. So the

Set ? = ?

is wrong. That first ? won't work the way you might think it would. What it does is query winds up looking like this

"UPDATE Demo_table SET 'Mark' = 100 WHERE Name like 'DBSJ'"

where you actually wanted

"UPDATE Demo_table SET Mark = 100 WHERE Name like 'DBSJ'"

Notice the ticks around Mark in the first example? That is where it goes wrong, and you can't change that behaviour. (Although I believe you have "Mark" and "DBSJ" reveresed there.)

[hungleon88]

oh man!!it's exactly what you say.
so...there is no way to use the ? for table, colum name?? sad....

[masijade]

As I said, no.

Edit: Those are things that, if they absolutely must be dynamic, have to "cobbled" in i.e.

String a = "Mark";
String sql = "Set " + a + " = ?";

[hungleon88]

Thanks! But the code
String a = "Mark";
String sql = "Set " + a + " = ?";

not work.
error : Incorrect syntax near '='
T_T . Maybe when translate to SQL , it's doesn't work.

[masijade]

Show your entire SQL statement code.

[jason wang]

I think it should like this:

String str = " UPDATE Demo_table SET Mark = ? WHERE Name like ? ";
PrepareStatement preStm = cn.prepareStatement(str);
preStm.setDouble(1,100);
preStm.setString(2,"DBSJ");

I don't know whether the "Mark" is a column, if it is , then it should work.