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’)
|1||SELECT COUNT(*) FROM Transactions||Performs a full table scan. Slow on large tables.|
|2||SELECT CONVERT(bigint, rows)
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)
|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)
AND (index_id=0 or index_id=1);
|Quick (although not as fast as method 2) operation and equally important, reliable.|