From 1a844c380b83d94c70a735ee8035ce02c21f2df7 Mon Sep 17 00:00:00 2001
From: drh <drh@noemail.net>
Date: Wed, 4 Dec 2002 22:29:28 +0000
Subject: [PATCH] Fix a bug in the reverse scan logic that comes up when the
 table being scanned is empty.  Add additional tests for the reverse scan.
 (CVS 797)

FossilOrigin-Name: 0051c87d5e8d07fae09da2eb7b0d8cbd1bbd3c8e
---
 manifest        |  16 ++++----
 manifest.uuid   |   2 +-
 src/btree.c     |   7 ++--
 src/vdbe.c      |  16 ++++++--
 test/where.test | 101 +++++++++++++++++++++++++++++++++++++++++++++++-
 5 files changed, 125 insertions(+), 17 deletions(-)

diff --git a/manifest b/manifest
index ea9bcc9913..6c666c9e49 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Fixes\sto\sthe\slogic\sthat\sdecides\sif\sthe\sORDER\sBY\scan\sbe\signored\sdue\sto\sthe\nuse\sof\san\sindex.\s\sTests\supdated.\s(CVS\s796)
-D 2002-12-04T21:50:16
+C Fix\sa\sbug\sin\sthe\sreverse\sscan\slogic\sthat\scomes\sup\swhen\sthe\stable\sbeing\nscanned\sis\sempty.\s\sAdd\sadditional\stests\sfor\sthe\sreverse\sscan.\s(CVS\s797)
+D 2002-12-04T22:29:28
 F Makefile.in 868c17a1ae1c07603d491274cc8f86c04acf2a1e
 F Makefile.linux-gcc b86a99c493a5bfb402d1d9178dcdc4bd4b32f906
 F README f1de682fbbd94899d50aca13d387d1b3fd3be2dd
@@ -18,7 +18,7 @@ F main.mk 9d13839b9697af332d788fe6e801e68da027cc5c
 F publish.sh e5b83867d14708ed58cec8cba0a4f201e969474d
 F spec.template 238f7db425a78dc1bb7682e56e3834c7270a3f5e
 F sqlite.1 83f4a9d37bdf2b7ef079a82d54eaf2e3509ee6ea
-F src/btree.c 2ae69698a620c01b9cb88f447be01ab3e1e3355f
+F src/btree.c 215d4b322c98fbff795095fa253d9ea108d4b9de
 F src/btree.h 17710339f7a8f46e3c7d6d0d4648ef19c584ffda
 F src/build.c 415dce8886aabb6d45851caed7014707056d668b
 F src/delete.c aad9d4051ab46e6f6391ea5f7b8994a7c05bdd15
@@ -52,7 +52,7 @@ F src/tokenize.c 75e3bb37305b64e118e709752066f494c4f93c30
 F src/trigger.c 5ba917fc226b96065108da28186c2efaec53e481
 F src/update.c 881e4c8e7c786545da4fd2d95da19252b2e31137
 F src/util.c ca7650ef2cc2d50241e48029fca109a3016144ee
-F src/vdbe.c 84b224d0ecfb2555a976f074924dd3e6d3d91dfb
+F src/vdbe.c aa6165ae4f2303795e4c5531293576c541363e40
 F src/vdbe.h b7584044223104ba7896a7f87b66daebdd6022ba
 F src/where.c af235636b7bc7f7f42ee1c7162d1958ad0102cab
 F test/all.test 873d30e25a41b3aa48fec5633a7ec1816e107029
@@ -115,7 +115,7 @@ F test/update.test 7ffb062d580a972e7870d0f51d5af3ab9bfeae08
 F test/vacuum.test 059871b312eb910bbe49dafde1d01490cc2c6bbe
 F test/version.test 605fd0d7e7d571370c32b12dbf395b58953de246
 F test/view.test c64fa39ea57f3c2066c854290f032ad13b23b83d
-F test/where.test 9e6e7e0a8bc6eff879bf12a497d6529df7fa9852
+F test/where.test ffaa91611edb8961d887d02492aa13f82782ff66
 F tool/diffdb.c 7524b1b5df217c20cd0431f6789851a4e0cb191b
 F tool/lemon.c 022adc2830c2705828f744d2c59798bd462eb465
 F tool/lempar.c 73a991cc3017fb34804250fa901488b5147b3717
@@ -152,7 +152,7 @@ F www/speed.tcl a20a792738475b68756ea7a19321600f23d1d803
 F www/sqlite.tcl ae3dcfb077e53833b59d4fcc94d8a12c50a44098
 F www/tclsqlite.tcl 1db15abeb446aad0caf0b95b8b9579720e4ea331
 F www/vdbe.tcl 2013852c27a02a091d39a766bc87cff329f21218
-P c7a3487981de0ed5b43ea3ff4d46ab4437068dca
-R ad809775145f9a28c47c1aa04b1e5814
+P bfb9a2aa939ecffc5dc2c7c23bddd57d357bdf13
+R e8e5bb54da6e21aac3b570ab92f52726
 U drh
-Z 2d97197b4281b66cabb81cf1fc140ed8
+Z ef156328459f096ede699892581cbeef
diff --git a/manifest.uuid b/manifest.uuid
index f25a3cbbb1..1723f4a045 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-bfb9a2aa939ecffc5dc2c7c23bddd57d357bdf13
\ No newline at end of file
+0051c87d5e8d07fae09da2eb7b0d8cbd1bbd3c8e
\ No newline at end of file
diff --git a/src/btree.c b/src/btree.c
index 6554584c76..193c224d66 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -9,7 +9,7 @@
 **    May you share freely, never taking more than you give.
 **
 *************************************************************************
-** $Id: btree.c,v 1.74 2002/12/04 13:40:26 drh Exp $
+** $Id: btree.c,v 1.75 2002/12/04 22:29:28 drh Exp $
 **
 ** This file implements a external (disk-based) database using BTrees.
 ** For a detailed discussion of BTrees, refer to
@@ -1495,7 +1495,8 @@ int sqliteBtreeLast(BtCursor *pCur, int *pRes){
 ** this value is as follows:
 **
 **     *pRes<0      The cursor is left pointing at an entry that
-**                  is smaller than pKey.
+**                  is smaller than pKey or if the table is empty
+**                  and the cursor is therefore left point to nothing.
 **
 **     *pRes==0     The cursor is left pointing at an entry that
 **                  exactly matches pKey.
@@ -1513,7 +1514,7 @@ int sqliteBtreeMoveto(BtCursor *pCur, const void *pKey, int nKey, int *pRes){
     int lwr, upr;
     Pgno chldPg;
     MemPage *pPage = pCur->pPage;
-    int c = -1;
+    int c = -1;  /* pRes return if table is empty must be -1 */
     lwr = 0;
     upr = pPage->nCell-1;
     while( lwr<=upr ){
diff --git a/src/vdbe.c b/src/vdbe.c
index 93b4ee9342..58a5374767 100644
--- a/src/vdbe.c
+++ b/src/vdbe.c
@@ -36,7 +36,7 @@
 ** in this file for details.  If in doubt, do not deviate from existing
 ** commenting and indentation practices when changing or adding code.
 **
-** $Id: vdbe.c,v 1.186 2002/12/04 20:01:06 drh Exp $
+** $Id: vdbe.c,v 1.187 2002/12/04 22:29:29 drh Exp $
 */
 #include "sqliteInt.h"
 #include <ctype.h>
@@ -3394,9 +3394,17 @@ case OP_MoveTo: {
       if( res && pOp->p2>0 ){
         pc = pOp->p2 - 1;
       }
-    }else if( oc==OP_MoveLt && res>=0 ){
-      sqliteBtreePrevious(pC->pCursor, &res);
-      pC->recnoIsValid = 0;
+    }else if( oc==OP_MoveLt ){
+      if( res>=0 ){
+        sqliteBtreePrevious(pC->pCursor, &res);
+        pC->recnoIsValid = 0;
+      }else{
+        /* res might be negative because the table is empty.  Check to
+        ** see if this is the case.
+        */
+        int keysize;
+        res = sqliteBtreeKeySize(pC->pCursor,&keysize)!=0 || keysize==0;
+      }
       if( res && pOp->p2>0 ){
         pc = pOp->p2 - 1;
       }
diff --git a/test/where.test b/test/where.test
index 7a9f2d47db..32bd0d139b 100644
--- a/test/where.test
+++ b/test/where.test
@@ -11,7 +11,7 @@
 # This file implements regression tests for SQLite library.  The
 # focus of this file is testing the use of indices in WHERE clases.
 #
-# $Id: where.test,v 1.12 2002/12/04 21:50:16 drh Exp $
+# $Id: where.test,v 1.13 2002/12/04 22:29:29 drh Exp $
 
 set testdir [file dirname $argv0]
 source $testdir/tester.tcl
@@ -588,5 +588,104 @@ do_test where-7.14 {
     SELECT w FROM t1 WHERE x=3 AND y>100 AND y<196 ORDER BY y;
   }
 } {10 11 12 nosort}
+do_test where-7.15 {
+  cksort {
+    SELECT w FROM t1 WHERE x=3 AND y<81 ORDER BY y;
+  }
+} {nosort}
+do_test where-7.16 {
+  cksort {
+    SELECT w FROM t1 WHERE x=3 AND y<=81 ORDER BY y;
+  }
+} {8 nosort}
+do_test where-7.17 {
+  cksort {
+    SELECT w FROM t1 WHERE x=3 AND y>256 ORDER BY y;
+  }
+} {nosort}
+do_test where-7.18 {
+  cksort {
+    SELECT w FROM t1 WHERE x=3 AND y>=256 ORDER BY y;
+  }
+} {15 nosort}
+do_test where-7.19 {
+  cksort {
+    SELECT w FROM t1 WHERE x=3 AND y<81 ORDER BY y DESC;
+  }
+} {nosort}
+do_test where-7.20 {
+  cksort {
+    SELECT w FROM t1 WHERE x=3 AND y<=81 ORDER BY y DESC;
+  }
+} {8 nosort}
+do_test where-7.21 {
+  cksort {
+    SELECT w FROM t1 WHERE x=3 AND y>256 ORDER BY y DESC;
+  }
+} {nosort}
+do_test where-7.22 {
+  cksort {
+    SELECT w FROM t1 WHERE x=3 AND y>=256 ORDER BY y DESC;
+  }
+} {15 nosort}
+do_test where-7.23 {
+  cksort {
+    SELECT w FROM t1 WHERE x=0 AND y<4 ORDER BY y;
+  }
+} {nosort}
+do_test where-7.24 {
+  cksort {
+    SELECT w FROM t1 WHERE x=0 AND y<=4 ORDER BY y;
+  }
+} {1 nosort}
+do_test where-7.25 {
+  cksort {
+    SELECT w FROM t1 WHERE x=6 AND y>10201 ORDER BY y;
+  }
+} {nosort}
+do_test where-7.26 {
+  cksort {
+    SELECT w FROM t1 WHERE x=6 AND y>=10201 ORDER BY y;
+  }
+} {100 nosort}
+do_test where-7.27 {
+  cksort {
+    SELECT w FROM t1 WHERE x=0 AND y<4 ORDER BY y DESC;
+  }
+} {nosort}
+do_test where-7.28 {
+  cksort {
+    SELECT w FROM t1 WHERE x=0 AND y<=4 ORDER BY y DESC;
+  }
+} {1 nosort}
+do_test where-7.29 {
+  cksort {
+    SELECT w FROM t1 WHERE x=6 AND y>10201 ORDER BY y DESC;
+  }
+} {nosort}
+do_test where-7.30 {
+  cksort {
+    SELECT w FROM t1 WHERE x=6 AND y>=10201 ORDER BY y DESC;
+  }
+} {100 nosort}
+
+do_test where-8.1 {
+  execsql {
+    CREATE TABLE t4 AS SELECT * FROM t1;
+    CREATE INDEX i4xy ON t4(x,y);
+  }
+  cksort {
+    SELECT w FROM t4 WHERE x=4 and y<1000 ORDER BY y DESC limit 3;
+  }
+} {30 29 28 nosort}
+do_test where-8.2 {
+  execsql {
+    DELETE FROM t4;
+  }
+  cksort {
+    SELECT w FROM t4 WHERE x=4 and y<1000 ORDER BY y DESC limit 3;
+  }
+} {nosort}
+
 
 finish_test