From ac8eb11375458631836e42f43164e88c3f569df5 Mon Sep 17 00:00:00 2001
From: drh <drh@noemail.net>
Date: Thu, 17 Mar 2011 01:58:21 +0000
Subject: [PATCH] Comment enhancement to better explain the logic in the "x IS
 NULL" optimization.

FossilOrigin-Name: 869f894798a65f8bc0e0b083866a784fa0189f68
---
 manifest      | 18 +++++++++---------
 manifest.uuid |  2 +-
 src/where.c   |  3 ++-
 3 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/manifest b/manifest
index b04b624d6b..a9110cb28d 100644
--- a/manifest
+++ b/manifest
@@ -1,8 +1,8 @@
 -----BEGIN PGP SIGNED MESSAGE-----
 Hash: SHA1
 
-C Enhances\sto\sthe\squery\splanner\ssuch\sthat\s"x\sIS\sNULL"\sconstraints\stake\sthe\nSTAT2\sstatistics\sinto\saccount,\sjust\slike\s"x=VALUE"\sconstraints.
-D 2011-03-17T01:34:26.570
+C Comment\senhancement\sto\sbetter\sexplain\sthe\slogic\sin\sthe\s"x\sIS\sNULL"\s\noptimization.
+D 2011-03-17T01:58:21.662
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 27701a1653595a1f2187dc61c8117e00a6c1d50f
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -246,7 +246,7 @@ F src/vtab.c b297e8fa656ab5e66244ab15680d68db0adbec30
 F src/wal.c 7334009b396285b658a95a3b6bc6d2b016a1f794
 F src/wal.h 7a5fbb00114b7f2cd40c7e1003d4c41ce9d26840
 F src/walker.c 3112bb3afe1d85dc52317cb1d752055e9a781f8f
-F src/where.c a41a1c64aceb4138a865e6dc939f781f53401d68
+F src/where.c a6e89fe7e56ab7e633be6fdebdddd857e9e5bc99
 F test/aggerror.test a867e273ef9e3d7919f03ef4f0e8c0d2767944f2
 F test/alias.test 4529fbc152f190268a15f9384a5651bbbabc9d87
 F test/all.test 51756962d522e474338e9b2ebb26e7364d4aa125
@@ -917,14 +917,14 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
-P 3e984195f1f6d28734456dd726d226cedf207da2
-R 291ccee36a06fddbdbf66dee9d0c5dc8
+P 2353176811f752a16c1f2351a3d3431919b062a9
+R ceaf122e76347e0b045461abe9cbfd0f
 U drh
-Z 44243678e5ac002f859d95b6693267ff
+Z 6e216a7f32c457388fcc438c6cd929ce
 -----BEGIN PGP SIGNATURE-----
 Version: GnuPG v1.4.6 (GNU/Linux)
 
-iD8DBQFNgWUmoxKgR168RlERArUBAJ9O6MIvLSm72rE66pJVBmPTs+4oyACdHack
-G7nsgBYo5KQjyDA5i3CGse8=
-=owlC
+iD8DBQFNgWrBoxKgR168RlERAg4rAJ0ZbgbEbrWUz8iIL7EI7v8AcMLRpQCfZka3
+v7cQP/zk4VcNw9IakEHnWtw=
+=fknb
 -----END PGP SIGNATURE-----
diff --git a/manifest.uuid b/manifest.uuid
index 86fa92432e..9f597732d4 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-2353176811f752a16c1f2351a3d3431919b062a9
\ No newline at end of file
+869f894798a65f8bc0e0b083866a784fa0189f68
\ No newline at end of file
diff --git a/src/where.c b/src/where.c
index 0cda03f451..cdcaa98c01 100644
--- a/src/where.c
+++ b/src/where.c
@@ -2520,7 +2520,8 @@ range_est_fallback:
 ** an equality constraint x=VALUE and where that VALUE occurs in
 ** the histogram data.  This only works when x is the left-most
 ** column of an index and sqlite_stat2 histogram data is available
-** for that index.
+** for that index.  When pExpr==NULL that means the constraint is
+** "x IS NULL" instead of "x=VALUE".
 **
 ** Write the estimated row count into *pnRow and return SQLITE_OK. 
 ** If unable to make an estimate, leave *pnRow unchanged and return
-- 
2.47.2