How to check if a value already exists to avoid duplicates?If it exist then do nothing otherwise insert record into database

Question

I'm trying to check if an Id already exists in table before I insert a duplicate.

So I need to check the table of database for the presence of the Id and if it exists then do nothing Otherwise I want to insert the record into the table. How can i do this?

Is there any other way except this:

Sql_query->Select id from table where key="something";

If(true) 
{
  do nothing;
}
else
{
  Insert record in database;
}

I want to avoid this because it requires time to search entire table and then insert. So is there any feasible way?

Answer 1

Two strategies:

1. Let the database do this task. Alter your table so the field you want to be unique is actually a unique index . When you want to insert the data, and it is a duplicate, you'll receive an error which can be used to decide what to do next. Or you might use an ON DUPLICATE KEY if you want to do another table operation instead, if needed.
2. Query the table to find out if there the id is already present. If not, generate your insert.

Example:

$mysqli = new mysqli("localhost", "my_user", "my_password", "world");
$result = $mysqli->query("SELECT id FROM yourtable");
if ($result->num_rows > 0) {
    /* do your insert */
}
$result->close();

I prefer letting the database do the job.

Update:

On request here are two examples on how to add an unique index to your table. The SQL looks like this:

CREATE UNIQUE INDEX your index_name
ON your_table (your_id_field);

When inserting data, mysql will throw an error if the key already exists. To work with this error, do something like this:

$SQL = 'INSERT INTO yourtable (yourfield1, yourfield2) 
        VALUES ( 1, "Hello")';    
$result = $mysqli->query($SQL);

if (!mysqli_query($link, $SQL)) {
    if(mysqli_errno($link) == 1062) {
         /* duplicate ... whatever you want in this case */
    }
}

You don't need all this error handling if you don't want to do anything in this situation of course.

Answer 2

You can do that with the following code:

<?php
   if($stmt = $db->prepare("SELECT * FROM tablename WHERE id=?")){
    $stmt->bind_param('i', $id);
    $stmt->execute();
    $stmt->store_result();

    if($stmt->num_rows == 0){
      // CREATE RECORD
    }
   }
?>

You just need to search in the table and check if the query returns something

Answer 3

Create unique index on a column (if you are not checking the primary key) and use ON DUPLICATE when creatin SQL query. More about this: http://dev.mysql.com/doc/refman/5.0/en/insert-on-duplicate.html