From: drh <drh@noemail.net>
Date: Wed, 21 Mar 2018 01:59:46 +0000 (+0000)
Subject: Relax LEFT-JOIN restrictions on the push-down optimization.
X-Git-Tag: version-3.23.0~39^2
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=refs%2Fheads%2Fjoin-strength-reduction;p=thirdparty%2Fsqlite.git

Relax LEFT-JOIN restrictions on the push-down optimization.

FossilOrigin-Name: b5d3dd8cb0b1e42ed0671a12d22af05194ea9522e4f41fd4bb0deff70b8b0757
---

diff --git a/manifest b/manifest
index 83de169744..1e671d756c 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Do\sa\smore\sthorough\sjob\sof\scleaning\serasing\straces\sof\sthe\sstrength-reduced\nLEFT\sJOIN.
-D 2018-03-20T22:52:27.787
+C Relax\sLEFT-JOIN\srestrictions\son\sthe\spush-down\soptimization.
+D 2018-03-21T01:59:46.055
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F Makefile.in 7016fc56c6b9bfe5daac4f34be8be38d8c0b5fab79ccbfb764d3b23bf1c6fff3
@@ -489,7 +489,7 @@ F src/printf.c d3b7844ddeb11fbbdd38dd84d09c9c1ac171d21fb038473c3aa97981201cc660
 F src/random.c 80f5d666f23feb3e6665a6ce04c7197212a88384
 F src/resolve.c 66c73fcb7719b8ff0e841b58338f13604ff3e2b50a723f9b8f383595735262f6
 F src/rowset.c 7b7e7e479212e65b723bf40128c7b36dc5afdfac
-F src/select.c 926d122e87dcd82b3bb1c2fd5879163abc957916ae168ee91017ccd459fe58d5
+F src/select.c 2c408ab9b4bfc807e6a9d3d45337d20ebe72a8b7ac793854710bf9d572e7ab6d
 F src/shell.c.in 911b9e3bce40413c78fdba28efa28363e98183819bd4b300780bf57bacfc4b84
 F src/sqlite.h.in 19762b57baa1ade67531f254de94374428fb9c82452ef305017847945f9c2911
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
@@ -1712,7 +1712,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 5b7abecc7ab8ccbbb8cb5e0f672e67625c2555ad03442efbf34cb395f5bb71a8
-R 600bea19530f5a14859b1c8b3c822982
+P 08833dda3a25965cc509d0244d7cd68bdb2306351ca52862f347e1efe5db4508
+R ec5a139322d92c7ba66f92f44103e585
 U drh
-Z 1305d962d2e1b706271862008b361453
+Z 2e81978b7831515aef1bcc77d7672624
diff --git a/manifest.uuid b/manifest.uuid
index 9290b2b977..edbd073ade 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-08833dda3a25965cc509d0244d7cd68bdb2306351ca52862f347e1efe5db4508
\ No newline at end of file
+b5d3dd8cb0b1e42ed0671a12d22af05194ea9522e4f41fd4bb0deff70b8b0757
\ No newline at end of file
diff --git a/src/select.c b/src/select.c
index c4320c5c7f..ca3e8b7f05 100644
--- a/src/select.c
+++ b/src/select.c
@@ -390,7 +390,8 @@ static void setJoinExpr(Expr *p, int iTable){
 */
 static void unsetJoinExpr(Expr *p, int iTable){
   while( p ){
-    if( ExprHasProperty(p, EP_FromJoin) && p->iRightJoinTable==iTable ){
+    if( ExprHasProperty(p, EP_FromJoin)
+     && (iTable<0 || p->iRightJoinTable==iTable) ){
       ExprClearProperty(p, EP_FromJoin);
     }
     if( p->op==TK_FUNCTION && p->x.pList ){
@@ -3856,12 +3857,21 @@ static int flattenSubquery(
 **   (3) The inner query has a LIMIT clause (since the changes to the WHERE
 **       close would change the meaning of the LIMIT).
 **
-**   (4) The inner query is the right operand of a LEFT JOIN.  (The caller
-**       enforces this restriction since this routine does not have enough
-**       information to know.)
+**   (4) (** This restriction was removed on 2018-03-21.  It used to read:
+**       The inner query is the right operand of a LEFT JOIN. **)
 **
 **   (5) The WHERE clause expression originates in the ON or USING clause
-**       of a LEFT JOIN.
+**       of a LEFT JOIN where iCursor is not the right-hand table of that
+**       left join.  An example:
+**
+**           SELECT *
+**           FROM (SELECT 1 AS a1 UNION ALL SELECT 2) AS aa
+**           JOIN (SELECT 1 AS b2 UNION ALL SELECT 2) AS bb ON (a1=b2)
+**           LEFT JOIN (SELECT 8 AS c3 UNION ALL SELECT 9) AS cc ON (b2=2);
+**
+**       The correct answer is three rows:  (1,1,NULL),(2,2,8),(2,2,9).
+**       But if the (b2=2) term were to be pushed down into the bb subquery,
+**       then the (1,1,NULL) row would be suppressed.
 **
 ** Return 0 if no changes are made and non-zero if one or more WHERE clause
 ** terms are duplicated into the subquery.
@@ -3897,12 +3907,15 @@ static int pushDownWhereTerms(
     nChng += pushDownWhereTerms(pParse, pSubq, pWhere->pRight, iCursor);
     pWhere = pWhere->pLeft;
   }
-  if( ExprHasProperty(pWhere,EP_FromJoin) ) return 0; /* restriction (5) */
+  if( ExprHasProperty(pWhere,EP_FromJoin) && pWhere->iRightJoinTable!=iCursor ){
+    return 0; /* restriction (5) */
+  }
   if( sqlite3ExprIsTableConstant(pWhere, iCursor) ){
     nChng++;
     while( pSubq ){
       SubstContext x;
       pNew = sqlite3ExprDup(pParse->db, pWhere, 0);
+      unsetJoinExpr(pNew, -1);
       x.pParse = pParse;
       x.iTable = iCursor;
       x.iNewTable = iCursor;
@@ -5360,8 +5373,7 @@ int sqlite3Select(
     /* Make copies of constant WHERE-clause terms in the outer query down
     ** inside the subquery.  This can help the subquery to run more efficiently.
     */
-    if( (pItem->fg.jointype & JT_OUTER)==0
-     && OptimizationEnabled(db, SQLITE_PushDown)
+    if( OptimizationEnabled(db, SQLITE_PushDown)
      && pushDownWhereTerms(pParse, pSub, p->pWhere, pItem->iCursor)
     ){
 #if SELECTTRACE_ENABLED