Prevent an automatic index from taking the place of a declared index.

FossilOrigin-Name: 4ece839d445ff578a449a339ab579a32e64c9d28

test/autoindex3.test

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+# 2014-06-17
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#*************************************************************************
+#
+# This file implements regression tests for SQLite library.  The
+# focus of this script is testing automatic index creation logic,
+# and specifically that an automatic index will not be created that
+# shadows a declared index.
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+
+# The t1b and t2d indexes are not very selective.  It used to be that
+# the autoindex mechanism would create automatic indexes on t1(b) or
+# t2(d), make assumptions that they were reasonably selective, and use
+# them instead of t1b or t2d.  But that would be cheating, because the
+# automatic index cannot be any more selective than the real index.
+#
+# This test verifies that the cheat is no longer allowed.
+#
+do_execsql_test autoindex3-100 {
+  CREATE TABLE t1(a,b,x);
+  CREATE TABLE t2(c,d,y);
+  CREATE INDEX t1b ON t1(b);
+  CREATE INDEX t2d ON t2(d);
+  ANALYZE sqlite_master;
+  INSERT INTO sqlite_stat1 VALUES('t1','t1b','10000 500');
+  INSERT INTO sqlite_stat1 VALUES('t2','t2d','10000 500');
+  ANALYZE sqlite_master;
+  EXPLAIN QUERY PLAN SELECT * FROM t1, t2 WHERE d=b;
+} {~/AUTO/}
+
+# Automatic indexes can still be used if existing indexes do not
+# participate in == constraints.
+#
+do_execsql_test autoindex3-110 {
+  EXPLAIN QUERY PLAN SELECT * FROM t1, t2 WHERE d>b AND x=y;
+} {/AUTO/}
+do_execsql_test autoindex3-120 {
+  EXPLAIN QUERY PLAN SELECT * FROM t1, t2 WHERE d<b AND x=y;
+} {/AUTO/}
+do_execsql_test autoindex3-130 {
+  EXPLAIN QUERY PLAN SELECT * FROM t1, t2 WHERE d IS NULL AND x=y;
+} {/AUTO/}
+do_execsql_test autoindex3-140 {
+  EXPLAIN QUERY PLAN SELECT * FROM t1, t2 WHERE d IN (5,b) AND x=y;
+} {/AUTO/}
+
+
+finish_test