Faster alternative in Oracle to SELECT COUNT(*) FROM sometable

I've notice that in Oracle, the query

SELECT COUNT(*) FROM sometable;

is very slow for large tables. It seems like the database it actually going through every row and incrementing a counter one at a time. I would think that there would be a counter somewhere in the table how many rows that table has.

So if I want to check the number of rows in a table in Oracle, what is the fastest way to do that?

Solution 1:

If you want just a rough estimate, you can extrapolate from a sample:

SELECT COUNT(*) * 100 FROM sometable SAMPLE (1);

For greater speed (but lower accuracy) you can reduce the sample size:

SELECT COUNT(*) * 1000 FROM sometable SAMPLE (0.1);

For even greater speed (but even worse accuracy) you can use block-wise sampling:

SELECT COUNT(*) * 100 FROM sometable SAMPLE BLOCK (1);

Solution 2:

This works great for large tables.

SELECT NUM_ROWS FROM ALL_TABLES WHERE TABLE_NAME = 'TABLE_NAME_IN_UPPERCASE';

For small to medium size tables, following will be ok.

SELECT COUNT(Primary_Key) FROM table_name;

Cheers,