if statement doesn't work

In Wordpress, I'm trying to add the post ID of posts I publish in a new table if not already there (to avoid double entries when updating posts from the admin panel)

if( $wpdb->get_row("SELECT post_id FROM wp_post_votes WHERE post_id != $post_ID" ) ) {
    $wpdb->insert( $wpdb->prefix . 'post_votes', array( 'post_id' => $post_ID ) );
    }

This statement works only with a = operator and an "else ( do code.. }". 开发者_Python百科With != nothing happens I can't figure out why.. I just want to keep the code as short as possible.

if(!($wpdb->get_row("SELECT post_id FROM wp_post_votes WHERE post_id = $post_ID" ) ) ) {
    $wpdb->insert( $wpdb->prefix . 'post_votes', array( 'post_id' => $post_ID ) );
}

Should be what you're looking for. (Added a ! before the conditional to simulate your "else" effect)

Try

if( !$wpdb->get_row("SELECT post_id FROM wp_post_votes WHERE post_id = $post_ID" )

Your if statement is checking that the output from

$wpdb->get_row("SELECT post_id FROM wp_post_votes WHERE post_id != $post_ID" )

evaluates to a true-like value. You're essentially running a query that selects all IDs from ALL rows (except for perhaps one). This is inefficient and probably not what you wanted - you probably wanted to check if a matching row was not found, not that non-matching rows were found.

You probably want:

if (!$wpdb->get_row("SELECT post_id FROM wp_post_votes WHERE post_id = $post_ID" )) {