Implementing TABLESAMPLE clause for PostgreSQL

by Huang Qi Victor for PostgreSQL Project

TABLESAMPLE is an interesting sql clause. It is defined in SQL standard 2003. An example is SELECT avg(salary) FROM emp TABLESAMPLE SYSTEM (50); It will return a sample of the underlying table of which the size depends on the number specified in the bracket. The SQL standard of TABLESAMPLE clause can be found at <http://www.neilconway.org/talks/hacking/ottawa/sql_standard.pdf>. Microsoft SQL Server and DB2 have implemented this clause. Querying a sample of a table is often occurring in people’s work. Looking at the page: <www.almaden.ibm.com/cs/people/peterh/idugjbig.pdf>. In page 1 and 2, the author described the benefits and usage of a fast sampling method towards the discovering general trends and patterns in data. It will be useful for PostgreSQL to implement this feature and make it available to the users.