SQL Server–HOW-TO: quickly retrieve accurate row count for table fast sql count

por | 14 octubre, 2015

Rate This


15 Jul 2010 1:24 PM

Recently, I’ve been involved in a very interesting project in which we need to perform operations on a table containing 3,000,000,000+ rows. For some tooling, I needed a quick and reliable way to count the number of rows contained within this table. Performing a simple

SELECT COUNT(*) FROM Transactions

operation would do the trick on small tables with low IO, but what’s the ‘best’ way (quick and reliable) to perform this operation on large tables?

I searched and found different answers, which I note here so it might be of use to someone… (My table was called ‘Transactions’)

Index Query Comment
1 SELECT COUNT(*) FROM Transactions Performs a full table scan. Slow on large tables.
2 SELECT CONVERT(bigint, rows)

FROM sysindexes

WHERE id = OBJECT_ID(‘Transactions’)

AND indid < 2

Fast way to retrieve row count. Depends on statistics and is inaccurate.

Run DBCC UPDATEUSAGE(Database) WITH COUNT_ROWS, which can take significant time for large tables.

3 SELECT CAST(p.rows AS float)

FROM sys.tables AS tbl

INNER JOIN sys.indexes AS idx ON idx.object_id = tbl.object_id and idx.index_id < 2

INNER JOIN sys.partitions AS p ON p.object_id=CAST(tbl.object_id AS int)

AND p.index_id=idx.index_id

WHERE ((tbl.name=N’Transactions’

AND SCHEMA_NAME(tbl.schema_id)=’dbo’))

The way the SQL management studio counts rows (look at table properties, storage, row count). Very fast, but still an approximate number of rows.
4 SELECT SUM (row_count)

FROM sys.dm_db_partition_stats

WHERE object_id=OBJECT_ID(‘Transactions’)

AND (index_id=0 or index_id=1);

Quick (although not as fast as method 2) operation and equally important, reliable.

SQL Server