What does `select 100 * (sum(idx_blks_

What does

select 100 * (sum(idx_blks_hit) - sum(idx_blks_read)) / sum(idx_blks_hit) as index_hit_rate FROM pg_statio_user_indexes;

select 100 * (sum(idx_blks_hit) - sum(idx_blks_read)) / sum(idx_blks_hit) as index_hit_rate FROM pg_statio_user_indexes;

select 100 * (sum(idx_blks_hit) - sum(idx_blks_read)) / sum(idx_blks_hit) as index_hit_rate FROM pg_statio_user_indexes;

select 100 * (sum(idx_blks_hit) - sum(idx_blks_read)) / sum(idx_blks_hit) as index_hit_rate FROM pg_statio_user_indexes; show?