The simplest form of summary is counting: ''how many'' records were retrieved?  A simple overall count is done by using ''count(*)'' as the thing to select (or ''project'', in formal relational algebraic terms):
 
The simplest form of summary is counting: ''how many'' records were retrieved?  A simple overall count is done by using ''count(*)'' as the thing to select (or ''project'', in formal relational algebraic terms):
   −
  select count(*) from movie where year like '200%';
+
  select count(*) from movie where year > 2000
   Unexpected non-MediaWiki exception encountered, of type "Error"
Error: Call to undefined function each() in /apps/xmlpipedb/biodb/fall2013/includes/diff/DairikiDiff.php:374
Stack trace:
#0 /apps/xmlpipedb/biodb/fall2013/includes/diff/DairikiDiff.php(480): _DiffEngine->_diag()
#1 /apps/xmlpipedb/biodb/fall2013/includes/diff/DairikiDiff.php(291): _DiffEngine->_compareseq()
#2 /apps/xmlpipedb/biodb/fall2013/includes/diff/DairikiDiff.php(175): _DiffEngine->diff_local()
#3 /apps/xmlpipedb/biodb/fall2013/includes/diff/DairikiDiff.php(653): _DiffEngine->diff()
#4 /apps/xmlpipedb/biodb/fall2013/includes/diff/DairikiDiff.php(820): Diff->__construct()
#5 /apps/xmlpipedb/biodb/fall2013/includes/diff/DairikiDiff.php(1240): MappedDiff->__construct()
#6 /apps/xmlpipedb/biodb/fall2013/includes/diff/DairikiDiff.php(1458): WordLevelDiff->__construct()
#7 /apps/xmlpipedb/biodb/fall2013/includes/diff/DairikiDiff.php(952): TableDiffFormatter->_changed()
#8 /apps/xmlpipedb/biodb/fall2013/includes/diff/DairikiDiff.php(895): DiffFormatter->_block()
#9 /apps/xmlpipedb/biodb/fall2013/includes/diff/DifferenceEngine.php(765): DiffFormatter->format()
#10 /apps/xmlpipedb/biodb/fall2013/includes/diff/DifferenceEngine.php(655): DifferenceEngine->generateDiffBody()
#11 /apps/xmlpipedb/biodb/fall2013/includes/diff/DifferenceEngine.php(593): DifferenceEngine->getDiffBody()
#12 /apps/xmlpipedb/biodb/fall2013/includes/diff/DifferenceEngine.php(566): DifferenceEngine->getDiff()
#13 /apps/xmlpipedb/biodb/fall2013/includes/diff/DifferenceEngine.php(409): DifferenceEngine->showDiff()
#14 /apps/xmlpipedb/biodb/fall2013/includes/Article.php(725): DifferenceEngine->showDiffPage()
#15 /apps/xmlpipedb/biodb/fall2013/includes/Article.php(478): Article->showDiffPage()
#16 /apps/xmlpipedb/biodb/fall2013/includes/actions/ViewAction.php(37): Article->view()
#17 /apps/xmlpipedb/biodb/fall2013/includes/Wiki.php(427): ViewAction->show()
#18 /apps/xmlpipedb/biodb/fall2013/includes/Wiki.php(304): MediaWiki->performAction()
#19 /apps/xmlpipedb/biodb/fall2013/includes/Wiki.php(536): MediaWiki->performRequest()
#20 /apps/xmlpipedb/biodb/fall2013/includes/Wiki.php(446): MediaWiki->main()
#21 /apps/xmlpipedb/biodb/fall2013/index.php(59): MediaWiki->run()
#22 {main}