How does $wpdb->get_var work with offset?

Question

In WordPress documentation, it says:

(https://codex.wordpress.org/Class_Reference/wpdb)

SELECT a Variable The get_var function returns a single variable from the database. Though only one variable is returned, the entire result of the query is cached for later use. Returns NULL if no result is found.

get_var( 'query', column_offset, row_offset ); ?>

query (string) The query you wish to run. Setting this parameter to null will return the specified variable from the cached results of the previous query. column_offset (integer) The desired column (0 being the first). Defaults to 0. row_offset (integer) The desired row (0 being the first). Defaults to 0.

My query is, can you please explain this line:

Setting this parameter to null will return the specified variable from the cached results of the previous query.

Which variable? If i code:

<?php $wpdb->get_var( null, column_offset, row_offset ); ?> 

Which variables value is it talking about?

Thanks.

Answer 1

You must specify values for column_offset and row_offset. For example:

 <?php $wpdb->get_var( null, 5, 0 ); ?> 

Will return "Hello World" (see attached image) But for that to work you had to have a previous query like this:

 <?php $wpdb->get_var( "SELECT * FROM $wpdb->posts" ); ?>