How many rows are there in a table?
There is no limit on the number of rows in a table but it is limited to available disk space and memory/swap space. If you are storing rows that exceed 2 KB aggregated data size, then the maximum number of rows may be limited to 4 billion or less.
Counting is one of the easiest SQL statements, so it is also many people's first experience of a PostgreSQL query.
How to do it…
From any interface, the SQL command used to count rows is as follows:
SELECT count(*) FROM table;This will return a single integer value as the result.
In psql, the command looks like the following:
postgres=# select count(*) from orders; count ------- 345 (1 row)
How it works...
PostgreSQL can choose between two techniques available to compute the SQL count(*) function. Both are available in all the currently supported versions:
- The first is called sequential scan. We access every data block in the table one after the other, reading the number of rows in each block. If the table is on the disk...