A question about insert?

Question

if the two applications want to insert the same data into database at the same time? but I only expect one application execute successful.
how do I prevent insert the same data into database?

Answer 1

if the two applications want to insert the same data
into database at the same time? but I only expect one
application execute successful.
how do I prevent insert the same data into database?This is not an advanced language topic and the language is
barely English, but allright. Here goes;
To prevent the insertion of equivalent data into the same
database you should find out about your database's transaction
mechanisme (if it has one). If it doesn't you should look
into mutual exclusion points in your client code.
What I mean is, that you want to examine before you insert,
and do this inside a protected timewindow. This can be achieved
inside your database with the use of transactions, or it can
be achieved inside your client code (if you're the only client
to that database and both calls live inside the same JVM)
by synchronization.
in pseudo code:
static Object mutex = new Object();
synchronized (mutex) {
  Object[] result;
  result = sqlselect("select * from table where foo=bar;");
  if (result.length == 0) {
    sqlinsert("insert into table (foo="bar");");
}