how to check wordpress custom table is empty or not [duplicate]

Answer 1

Using wordpress's WPDB class get_results() method will give you the data in form of object/array, you just need to check the count for $result which holds the result from get_results()

if(count($result) == 0){
// your code
}

See WPDB usage details

Answer 2

Try this :)

<?php
function schools_post_function()
{
    global $wpdb;
    $result = $wpdb->get_results("SELECT postid from wp_school_post WHERE `postid` IS NOT NULL");
    if(count($result) == 0)
    {
        echo "not filled";
    }
    else
    {
        echo "filled";

    }
}
?>

Answer 3

You could simplify your code and save resources using get_var instead to obtain the row count:

$count = $wpdb->get_var("SELECT COUNT(*)
    FROM {$wpdb->prefix}school_post WHERE postid IS NOT NULL");

if($count == 0)
{
    // No rows.
}