One quesion on number of rows and number of blocks

 

Hi All, My DB is 11.1. I think the number of blocks for a table can be calculated like this :number of blocks = (number of rows* avg_row_len)/block_size. And in my case, it is (867180*74)/(16*1024) = 3916. But when I checked its number of blocks from dba_tables, I found it was 1800. I collected the statistics on the table just before the check. It's easy to explain that the blocks are more than expected. But I don't know why it was far less than expected in this case. Could someone give me some advice, please? Best regards, Leon