Compression is applied on the column level and not on rows. As the name states, it compresses repeated values in a table with NULL, 0, and space. So, what really happens when we issue a compression statement?
In our recipe, the date column takes 4 bytes of space in the table. That means it will occupy 4 bytes of space. Our date column has 6 different values; of them, two are repeating, which are '2017-09-01'and'2017-09-05'. So by applying the MVC technique, Teradata will replace these values with presence bits 01 for ‘2017-09-01’ and 11 for ‘2017-09-05’; that means only 2 bits instead of 1 byte. These bits are stored in the table header, and when these values are referred to the optimizer replaces these bits with actual values ...
