Fastest way to count exact number of rows in a very large table?

The fastest way by far on MySQL is:

SHOW TABLE STATUS;

You will instantly get all your tables with the row count (which is the total) along with plenty of extra information if you want.


I got this script from another StackOverflow question/answer:

SELECT SUM(p.rows) FROM sys.partitions AS p
  INNER JOIN sys.tables AS t
  ON p.[object_id] = t.[object_id]
  INNER JOIN sys.schemas AS s
  ON s.[schema_id] = t.[schema_id]
  WHERE t.name = N'YourTableNameHere'
  AND s.name = N'dbo'
  AND p.index_id IN (0,1);

My table has 500 million records and the above returns in less than 1ms. Meanwhile,

SELECT COUNT(id) FROM MyTable

takes a full 39 minutes, 52 seconds!

They yield the exact same number of rows (in my case, exactly 519326012).

I do not know if that would always be the case.


Simple answer:

  • Database vendor independent solution = use the standard = COUNT(*)
  • There are approximate SQL Server solutions but don't use COUNT(*) = out of scope

Notes:

COUNT(1) = COUNT(*) = COUNT(PrimaryKey) just in case

Edit:

SQL Server example (1.4 billion rows, 12 columns)

SELECT COUNT(*) FROM MyBigtable WITH (NOLOCK)
-- NOLOCK here is for me only to let me test for this answer: no more, no less

1 runs, 5:46 minutes, count = 1,401,659,700

--Note, sp_spaceused uses this DMV
SELECT
   Total_Rows= SUM(st.row_count)
FROM
   sys.dm_db_partition_stats st
WHERE
    object_name(object_id) = 'MyBigtable' AND (index_id < 2)

2 runs, both under 1 second, count = 1,401,659,670

The second one has less rows = wrong. Would be the same or more depending on writes (deletes are done out of hours here)

Tags:

Database

Sql

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