Add documentation on the EXISTS expression. Ticket #1082. (CVS 2353)

FossilOrigin-Name: 76cacb4a39d2dd79a27624a8bd1ff65eeedd4ac8

manifest

@@ -1,5 +1,5 @@
-C Remove\sduplicate\sword\sfrom\sdocumentation.\s\sTicket\s#1103.\s(CVS\s2352)
-D 2005-02-19T12:32:57
+C Add\sdocumentation\son\sthe\sEXISTS\sexpression.\s\sTicket\s#1082.\s(CVS\s2353)
+D 2005-02-19T12:44:16
 F Makefile.in 76443a83549d1539105e12d13bd0054a05ab2214
 F Makefile.linux-gcc a9e5a0d309fa7c38e7c14d3ecf7690879d3a5457
 F README a01693e454a00cc117967e3f9fdab2d4d52e9bc1
@@ -257,7 +257,7 @@ F www/faq.tcl 1e348dec52dc0f21f4216fd6918c69c56daa4cfd
 F www/fileformat.tcl 900c95b9633abc3dcfc384d9ddd8eb4876793059
 F www/formatchng.tcl bfbf14dbf5181e771d06da7797767b0200b36d8a
 F www/index.tcl e4e44a17a73510fdb5de7d3002815e7524e23433
-F www/lang.tcl fad1d8d12b6c4e5185d9ca12c31c5cf7309b615c
+F www/lang.tcl 0e5aeb09864b9ae0746d8afaa6377193f1553486
 F www/lockingv3.tcl f59b19d6c8920a931f096699d6faaf61c05db55f
 F www/mingw.tcl d96b451568c5d28545fefe0c80bee3431c73f69c
 F www/nulls.tcl ec35193f92485b87b90a994a01d0171b58823fcf
@@ -274,7 +274,7 @@ F www/tclsqlite.tcl e73f8f8e5f20e8277619433f7970060ab01088fc
 F www/vdbe.tcl 095f106d93875c94b47367384ebc870517431618
 F www/version3.tcl 092a01f5ef430d2c4acc0ae558d74c4bb89638a0
 F www/whentouse.tcl 3e522a06ad41992023c80ca29a048ae2331ca5bd
-P 173aeb256e2c09098a4392874f8623e8a760d951
-R f9212a99a84060ce314d0381c1afc5ba
+P c1fc0a8aa96d2bd615f815b2477b801bda9e9c50
+R 058fc001a82eb2a82cc843693727b03a
 U drh
-Z abd4f7a0c7d7a614def59e6a3e63adf5
+Z ef9a2bd579709be8b4e9198f4f3f3df9

manifest.uuid

@@ -1 +1 @@
-c1fc0a8aa96d2bd615f815b2477b801bda9e9c50
+76cacb4a39d2dd79a27624a8bd1ff65eeedd4ac8

www/lang.tcl

@@ -1,7 +1,7 @@
 #
 # Run this Tcl script to generate the lang-*.html files.
 #
-set rcsid {$Id: lang.tcl,v 1.83 2005/02/14 06:38:41 danielk1977 Exp $}
+set rcsid {$Id: lang.tcl,v 1.84 2005/02/19 12:44:16 drh Exp $}
 source common.tcl
 
 if {[llength $argv]>0} {
@@ -903,7 +903,7 @@ Syntax {expr} {
 <expr> [NOT] IN ( <value-list> ) |
 <expr> [NOT] IN ( <select-statement> ) |
 <expr> [NOT] IN [<database-name> .] <table-name> |
-( <select-statement> ) |
+[EXISTS] ( <select-statement> ) |
 CASE [<expr>] LP WHEN <expr> THEN <expr> RPPLUS [ELSE <expr>] END
 } {like-op} {
 LIKE | NOT LIKE
@@ -1021,13 +1021,20 @@ of a row key in an UPDATE or INSERT statement.
 "SELECT * ..." does not return the row key.</p>
 
 <p>SELECT statements can appear in expressions as either the
-right-hand operand of the IN operator or as a scalar quantity.
-In both cases, the SELECT should have only a single column in its
+right-hand operand of the IN operator, as a scalar quantity, or
+as the operand of an EXISTS operator.
+As a scalar quantity or the operand of an IN operator,
+the SELECT should have only a single column in its
 result.  Compound SELECTs (connected with keywords like UNION or
 EXCEPT) are allowed.
-A SELECT in an expression is evaluated once before any other processing
-is performed, so none of the expressions within the select itself can
-refer to quantities in the containing expression.</p>
+With the EXISTS operator, the columns in the result set of the SELECT are
+ignored and the expression returns TRUE if one or more rows exist
+and FALSE if the result set is empty.
+If no terms in the SELECT expression refer to value in the containing
+query, then the expression is evaluated once prior to any other
+processing and the result is reused as necessary.  If the SELECT expression
+does contain variables from the outer query, then the SELECT is reevaluated
+every time it is needed.</p>
 
 <p>When a SELECT is the right operand of the IN operator, the IN
 operator returns TRUE if the result of the left operand is any of