Query optimizer enhancement: In "FROM a,b,c left join d" allow the C table

to be reordered with A and B.  This used to be the case but the capability
was removed by (3203) and (3052) in response to ticket #1652.  This change
restores the capability. (CVS 3529)

FossilOrigin-Name: 7393c81b8cb9d4344ae744de9eabcb3af64f1db8

manifest

@@ -1,5 +1,5 @@
-C Fix\sa\sbug\sin\slemon\sthat\sleads\sto\san\sassertion\sfault\sgiven\san\sinvalid\ngrammar.\s\sThe\sbug\sand\sthis\sfix\sdo\snot\seffect\son\sSQLite.\s\sTicket\s#2107.\s(CVS\s3528)
+C Query\soptimizer\senhancement:\sIn\s"FROM\sa,b,c\sleft\sjoin\sd"\sallow\sthe\sC\stable\nto\sbe\sreordered\swith\sA\sand\sB.\s\sThis\sused\sto\sbe\sthe\scase\sbut\sthe\scapability\nwas\sremoved\sby\s(3203)\sand\s(3052)\sin\sresponse\sto\sticket\s#1652.\s\sThis\schange\nrestores\sthe\scapability.\s(CVS\s3529)
-D 2006-12-14T01:06:22
+D 2006-12-16T16:25:15
 F Makefile.in 8e14898d41a53033ecb687d93c9cd5d109fb9ae3
 F Makefile.linux-gcc 2d8574d1ba75f129aba2019f0b959db380a90935
 F README 9c4e2d6706bdcc3efdd773ce752a8cdab4f90028
@@ -59,13 +59,13 @@ F src/attach.c b11eb4d5d3fb99a10a626956bccc7215f6b68b16
 F src/auth.c 902f4722661c796b97f007d9606bd7529c02597f
 F src/btree.c 116f748ee11ba4d3630882102e99b60ff58d2a84
 F src/btree.h 061c50e37de7f50b58528e352d400cf33ead7418
-F src/build.c 7199949a6a3449e9ec69408cc79a48ed04fd0b85
+F src/build.c 02aedde724dc73295d6e9b8dc29afb5dd38de507
 F src/callback.c fd9bb39f7ff6b52bad8365617abc61c720640429
 F src/complete.c 7d1a44be8f37de125fcafd3d3a018690b3799675
 F src/date.c 9602457c49210f77f860d1919a8249a3118cd43f
 F src/delete.c 804384761144fe1a5035b99f4bd7d706976831bd
 F src/experimental.c 1b2d1a6cd62ecc39610e97670332ca073c50792b
-F src/expr.c 03420f31394b45a601c8aff5dd445c4e0d58999b
+F src/expr.c 82603dc2882797734882507ed95dfcb7f7c583e3
 F src/func.c af537156dfeb91dbac8ffed4db6c4fa1a3164cc9
 F src/hash.c 449f3d6620193aa557f5d86cbc5cc6b87702b185
 F src/hash.h 1b3f7e2609141fd571f62199fc38687d262e9564
@@ -87,17 +87,17 @@ F src/os_win.c cac5f9b60faacd46874aa8dfefdb7dc4d0437ff9
 F src/os_win.h 41a946bea10f61c158ce8645e7646b29d44f122b
 F src/pager.c 18c9cb43b3e740c63eaa13da41c52926012e4853
 F src/pager.h 2e6d42f4ae004ae748a037b8468112b851c447a7
-F src/parse.y 8c79a1debbd92a4f5609511e9bf0222de78f5ecb
+F src/parse.y 9b3d1c0f8af81fe0cc909baf226865baa725bb23
 F src/pragma.c d0891d3504b6291b506a5ec2226bbf79ffcef003
 F src/prepare.c f4f45b4560defbb566cf8255763625d2c09a8023
 F src/printf.c b179b6ed12f793e028dd169e2e2e2b2a37eedc63
 F src/random.c d40f8d356cecbd351ccfab6eaedd7ec1b54f5261
-F src/select.c 6ba6d8ead43d0575ce1f8b418cc039f8f301389a
+F src/select.c 52f09127b53697b1a95835a9b0db9309cca8079f
 F src/server.c 087b92a39d883e3fa113cae259d64e4c7438bc96
 F src/shell.c 934cdcf67eccee6f5c1be87c98a477a2e263db3c
 F src/sqlite.h.in 2931f7ee2415e7a49fd12f386c23575046f0f540
 F src/sqlite3ext.h 2c2156cc32a158e2b7bd9042d42accf94bff2e40
-F src/sqliteInt.h f6bac44ee7b8ee2614b046974551c22999ec674f
+F src/sqliteInt.h 28d060f44a4a3ad1acb47bf1cef627c86ec45f5f
 F src/table.c 6d0da66dde26ee75614ed8f584a1996467088d06
 F src/tclsqlite.c e029f739bed90071789fe81a226d53e97a80a4d8
 F src/test1.c 19786ff3274635b6eac27a89f842416f388f3654
@@ -129,7 +129,7 @@ F src/vdbeaux.c 05cc6f0f82b86dfb4c356e06ab07ec8cc83a2eda
 F src/vdbefifo.c 9efb94c8c3f4c979ebd0028219483f88e57584f5
 F src/vdbemem.c 26623176bf1c616aa478da958fac49502491a921
 F src/vtab.c aa30e940058ea56a1b7a9a7019ec21d307316fb4
-F src/where.c 6e215af5a7b1eb2fc1b9d6fa653064753a84757f
+F src/where.c b34cc2c7f753cdf76aa37a71e579c2e266e50958
 F tclinstaller.tcl 046e3624671962dc50f0481d7c25b38ef803eb42
 F test/aggerror.test a867e273ef9e3d7919f03ef4f0e8c0d2767944f2
 F test/all.test b62fcd122052efaff1b0979aefa2dd65cfc8ee52
@@ -350,7 +350,7 @@ F test/vtab9.test 87afba55339b0c255e9697fbfb5bfb6120505d9d
 F test/vtab_err.test c07f7665dd90bc757f80f05e7951d826eda9bc48
 F test/where.test ee7c9a6659b07e1ee61177f6e7ff71565ee2c9df
 F test/where2.test 61d5b20d9bedc8788a773bbdc5b2ef887725928e
-F test/where3.test 3b5ad2c58069e12be2bd86bc5e211a82810521aa
+F test/where3.test 0a30fe9808b0fa01c46d0fcf4fac0bf6cf75bb30
 F tool/diffdb.c 7524b1b5df217c20cd0431f6789851a4e0cb191b
 F tool/lemon.c c200a81e346853c2902d5c43de8274af627a72bb
 F tool/lempar.c 0a2a5cf96a98a64a5594625ad8fbdbe41dbaca50
@@ -423,7 +423,7 @@ F www/tclsqlite.tcl bb0d1357328a42b1993d78573e587c6dcbc964b9
 F www/vdbe.tcl 87a31ace769f20d3627a64fa1fade7fed47b90d0
 F www/version3.tcl 890248cf7b70e60c383b0e84d77d5132b3ead42b
 F www/whentouse.tcl 97e2b5cd296f7d8057e11f44427dea8a4c2db513
-P 5f21c3a5f02b4f2c4550f5904e9d0e1e2eafb0f3
+P f2ad230f6dce98d664370d77845b5f585de20f08
-R ff4e890d4e50d38dfc084d0df0ba3d75
+R c3b5c634dcadafbfe73caa00b5b83dd9
 U drh
-Z c7ee88553b14e37d6f61a63315c281d7
+Z 31988b25529ff3c6bbd95097777774bb

manifest.uuid

@@ -1 +1 @@
-f2ad230f6dce98d664370d77845b5f585de20f08
+7393c81b8cb9d4344ae744de9eabcb3af64f1db8

src/build.c

@@ -22,7 +22,7 @@
 **     COMMIT
 **     ROLLBACK
 **
-** $Id: build.c,v 1.411 2006/09/11 23:45:49 drh Exp $
+** $Id: build.c,v 1.412 2006/12/16 16:25:15 drh Exp $
 */
 #include "sqliteInt.h"
 #include <ctype.h>
@@ -2940,15 +2940,6 @@ void sqlite3SrcListAssignCursors(Parse *pParse, SrcList *pList){
   }
 }
 
-/*
-** Add an alias to the last identifier on the given identifier list.
-*/
-void sqlite3SrcListAddAlias(SrcList *pList, Token *pToken){
-  if( pList && pList->nSrc>0 ){
-    pList->a[pList->nSrc-1].zAlias = sqlite3NameFromToken(pToken);
-  }
-}
-
 /*
 ** Delete an entire SrcList including all its substructure.
 */
@@ -2968,6 +2959,74 @@ void sqlite3SrcListDelete(SrcList *pList){
   sqliteFree(pList);
 }
 
+/*
+** This routine is called by the parser to add a new term to the
+** end of a growing FROM clause.  The "p" parameter is the part of
+** the FROM clause that has already been constructed.  "p" is NULL
+** if this is the first term of the FROM clause.  pTable and pDatabase
+** are the name of the table and database named in the FROM clause term.
+** pDatabase is NULL if the database name qualifier is missing - the
+** usual case.  If the term has a alias, then pAlias points to the
+** alias token.  If the term is a subquery, then pSubquery is the
+** SELECT statement that the subquery encodes.  The pTable and
+** pDatabase parameters are NULL for subqueries.  The pOn and pUsing
+** parameters are the content of the ON and USING clauses.
+**
+** Return a new SrcList which encodes is the FROM with the new
+** term added.
+*/
+SrcList *sqlite3SrcListAppendFromTerm(
+  SrcList *p,             /* The left part of the FROM clause already seen */
+  Token *pTable,          /* Name of the table to add to the FROM clause */
+  Token *pDatabase,       /* Name of the database containing pTable */
+  Token *pAlias,          /* The right-hand side of the AS subexpression */
+  Select *pSubquery,      /* A subquery used in place of a table name */
+  Expr *pOn,              /* The ON clause of a join */
+  IdList *pUsing          /* The USING clause of a join */
+){
+  struct SrcList_item *pItem;
+  p = sqlite3SrcListAppend(p, pTable, pDatabase);
+  if( p==0 || p->nSrc==0 ){
+    sqlite3ExprDelete(pOn);
+    sqlite3IdListDelete(pUsing);
+    sqlite3SelectDelete(pSubquery);
+    return p;
+  }
+  pItem = &p->a[p->nSrc-1];
+  if( pAlias && pAlias->n ){
+    pItem->zAlias = sqlite3NameFromToken(pAlias);
+  }
+  pItem->pSelect = pSubquery;
+  pItem->pOn = pOn;
+  pItem->pUsing = pUsing;
+  return p;
+}
+
+/*
+** When building up a FROM clause in the parser, the join operator
+** is initially attached to the left operand.  But the code generator
+** expects the join operator to be on the right operand.  This routine
+** Shifts all join operators from left to right for an entire FROM
+** clause.
+**
+** Example: Suppose the join is like this:
+**
+**           A natural cross join B
+**
+** The operator is "natural cross join".  The A and B operands are stored
+** in p->a[0] and p->a[1], respectively.  The parser initially stores the
+** operator with A.  This routine shifts that operator over to B.
+*/
+void sqlite3SrcListShiftJoinType(SrcList *p){
+  if( p && p->a ){
+    int i;
+    for(i=p->nSrc-1; i>0; i--){
+      p->a[i].jointype = p->a[i-1].jointype;
+    }
+    p->a[0].jointype = 0;
+  }
+}
+
 /*
 ** Begin a transaction
 */

src/expr.c

@@ -12,7 +12,7 @@
 ** This file contains routines used for analyzing expressions and
 ** for generating VDBE code that evaluates expressions in SQLite.
 **
-** $Id: expr.c,v 1.269 2006/11/23 11:59:13 drh Exp $
+** $Id: expr.c,v 1.270 2006/12/16 16:25:15 drh Exp $
 */
 #include "sqliteInt.h"
 #include <ctype.h>
@@ -891,22 +891,23 @@ static int lookupName(
             pExpr->iColumn = j==pTab->iPKey ? -1 : j;
             pExpr->affinity = pTab->aCol[j].affinity;
             pExpr->pColl = sqlite3FindCollSeq(db, ENC(db), zColl,-1, 0);
-            if( pItem->jointype & JT_NATURAL ){
+            if( i<pSrcList->nSrc-1 ){
-              /* If this match occurred in the left table of a natural join,
+              if( pItem[1].jointype & JT_NATURAL ){
-              ** then skip the right table to avoid a duplicate match */
+                /* If this match occurred in the left table of a natural join,
-              pItem++;
+                ** then skip the right table to avoid a duplicate match */
-              i++;
+                pItem++;
-            }
+                i++;
-            if( (pUsing = pItem->pUsing)!=0 ){
+              }else if( (pUsing = pItem[1].pUsing)!=0 ){
-              /* If this match occurs on a column that is in the USING clause
+                /* If this match occurs on a column that is in the USING clause
-              ** of a join, skip the search of the right table of the join
+                ** of a join, skip the search of the right table of the join
-              ** to avoid a duplicate match there. */
+                ** to avoid a duplicate match there. */
-              int k;
+                int k;
-              for(k=0; k<pUsing->nId; k++){
+                for(k=0; k<pUsing->nId; k++){
-                if( sqlite3StrICmp(pUsing->a[k].zName, zCol)==0 ){
+                  if( sqlite3StrICmp(pUsing->a[k].zName, zCol)==0 ){
-                  pItem++;
+                    pItem++;
-                  i++;
+                    i++;
-                  break;
+                    break;
+                  }
                 }
               }
             }

src/parse.y

@@ -14,7 +14,7 @@
 ** the parser.  Lemon will also generate a header file containing
 ** numeric codes for all of the tokens.
 **
-** @(#) $Id: parse.y,v 1.210 2006/09/21 11:02:17 drh Exp $
+** @(#) $Id: parse.y,v 1.211 2006/12/16 16:25:15 drh Exp $
 */
 
 // All token codes are small integers with #defines that begin with "TK_"
@@ -444,7 +444,10 @@ as(X) ::= .            {X.n = 0;}
 // A complete FROM clause.
 //
 from(A) ::= .                                 {A = sqliteMalloc(sizeof(*A));}
-from(A) ::= FROM seltablist(X).               {A = X;}
+from(A) ::= FROM seltablist(X).               {
+  A = X;
+  sqlite3SrcListShiftJoinType(A);
+}
 
 // "seltablist" is a "Select Table List" - the content of the FROM clause
 // in a SELECT statement.  "stl_prefix" is a prefix of this list.
@@ -455,31 +458,12 @@ stl_prefix(A) ::= seltablist(X) joinop(Y).    {
 }
 stl_prefix(A) ::= .                           {A = 0;}
 seltablist(A) ::= stl_prefix(X) nm(Y) dbnm(D) as(Z) on_opt(N) using_opt(U). {
-  A = sqlite3SrcListAppend(X,&Y,&D);
+  A = sqlite3SrcListAppendFromTerm(X,&Y,&D,&Z,0,N,U);
-  if( Z.n ) sqlite3SrcListAddAlias(A,&Z);
-  if( N ){
-    if( A && A->nSrc>1 ){ A->a[A->nSrc-2].pOn = N; }
-    else { sqlite3ExprDelete(N); }
-  }
-  if( U ){
-    if( A && A->nSrc>1 ){ A->a[A->nSrc-2].pUsing = U; }
-    else { sqlite3IdListDelete(U); }
-  }
 }
 %ifndef SQLITE_OMIT_SUBQUERY
   seltablist(A) ::= stl_prefix(X) LP seltablist_paren(S) RP
                     as(Z) on_opt(N) using_opt(U). {
-    A = sqlite3SrcListAppend(X,0,0);
+    A = sqlite3SrcListAppendFromTerm(X,0,0,&Z,S,N,U);
-    if( A && A->nSrc>0 ) A->a[A->nSrc-1].pSelect = S;
-    if( Z.n ) sqlite3SrcListAddAlias(A,&Z);
-    if( N ){
-      if( A && A->nSrc>1 ){ A->a[A->nSrc-2].pOn = N; }
-      else { sqlite3ExprDelete(N); }
-    }
-    if( U ){
-      if( A && A->nSrc>1 ){ A->a[A->nSrc-2].pUsing = U; }
-      else { sqlite3IdListDelete(U); }
-    }
   }
   
   // A seltablist_paren nonterminal represents anything in a FROM that
@@ -490,6 +474,7 @@ seltablist(A) ::= stl_prefix(X) nm(Y) dbnm(D) as(Z) on_opt(N) using_opt(U). {
   %destructor seltablist_paren {sqlite3SelectDelete($$);}
   seltablist_paren(A) ::= select(S).      {A = S;}
   seltablist_paren(A) ::= seltablist(F).  {
+     sqlite3SrcListShiftJoinType(F);
      A = sqlite3SelectNew(0,F,0,0,0,0,0,0,0);
   }
 %endif  SQLITE_OMIT_SUBQUERY

src/select.c

@@ -12,7 +12,7 @@
 ** This file contains C code routines that are called by the parser
 ** to handle SELECT statements in SQLite.
 **
-** $Id: select.c,v 1.322 2006/10/13 15:34:17 drh Exp $
+** $Id: select.c,v 1.323 2006/12/16 16:25:15 drh Exp $
 */
 #include "sqliteInt.h"
 
@@ -301,8 +301,8 @@ static int sqliteProcessJoin(Parse *pParse, Select *p){
     /* When the NATURAL keyword is present, add WHERE clause terms for
     ** every column that the two tables have in common.
     */
-    if( pLeft->jointype & JT_NATURAL ){
+    if( pRight->jointype & JT_NATURAL ){
-      if( pLeft->pOn || pLeft->pUsing ){
+      if( pRight->pOn || pRight->pUsing ){
         sqlite3ErrorMsg(pParse, "a NATURAL join may not have "
            "an ON or USING clause", 0);
         return 1;
@@ -320,7 +320,7 @@ static int sqliteProcessJoin(Parse *pParse, Select *p){
 
     /* Disallow both ON and USING clauses in the same join
     */
-    if( pLeft->pOn && pLeft->pUsing ){
+    if( pRight->pOn && pRight->pUsing ){
       sqlite3ErrorMsg(pParse, "cannot have both ON and USING "
         "clauses in the same join");
       return 1;
@@ -329,10 +329,10 @@ static int sqliteProcessJoin(Parse *pParse, Select *p){
     /* Add the ON clause to the end of the WHERE clause, connected by
     ** an AND operator.
     */
-    if( pLeft->pOn ){
+    if( pRight->pOn ){
-      setJoinExpr(pLeft->pOn, pRight->iCursor);
+      setJoinExpr(pRight->pOn, pRight->iCursor);
-      p->pWhere = sqlite3ExprAnd(p->pWhere, pLeft->pOn);
+      p->pWhere = sqlite3ExprAnd(p->pWhere, pRight->pOn);
-      pLeft->pOn = 0;
+      pRight->pOn = 0;
     }
 
     /* Create extra terms on the WHERE clause for each column named
@@ -342,8 +342,8 @@ static int sqliteProcessJoin(Parse *pParse, Select *p){
     ** Report an error if any column mentioned in the USING clause is
     ** not contained in both tables to be joined.
     */
-    if( pLeft->pUsing ){
+    if( pRight->pUsing ){
-      IdList *pList = pLeft->pUsing;
+      IdList *pList = pRight->pUsing;
       for(j=0; j<pList->nId; j++){
         char *zName = pList->a[j].zName;
         if( columnIndex(pLeftTab, zName)<0 || columnIndex(pRightTab, zName)<0 ){
@@ -1309,13 +1309,13 @@ static int prepSelectStmt(Parse *pParse, Select *p){
 
             if( i>0 ){
               struct SrcList_item *pLeft = &pTabList->a[i-1];
-              if( (pLeft->jointype & JT_NATURAL)!=0 &&
+              if( (pLeft[1].jointype & JT_NATURAL)!=0 &&
                         columnIndex(pLeft->pTab, zName)>=0 ){
                 /* In a NATURAL join, omit the join columns from the 
                 ** table on the right */
                 continue;
               }
-              if( sqlite3IdListIndex(pLeft->pUsing, zName)>=0 ){
+              if( sqlite3IdListIndex(pLeft[1].pUsing, zName)>=0 ){
                 /* In a join with a USING clause, omit columns in the
                 ** using clause from the table on the right. */
                 continue;
@@ -2175,7 +2175,7 @@ static int flattenSubquery(
   **
   ** which is not at all the same thing.
   */
-  if( pSubSrc->nSrc>1 && iFrom>0 && (pSrc->a[iFrom-1].jointype & JT_OUTER)!=0 ){
+  if( pSubSrc->nSrc>1 && (pSubitem->jointype & JT_OUTER)!=0 ){
     return 0;
   }
 
@@ -2192,8 +2192,7 @@ static int flattenSubquery(
   ** But the t2.x>0 test will always fail on a NULL row of t2, which
   ** effectively converts the OUTER JOIN into an INNER JOIN.
   */
-  if( iFrom>0 && (pSrc->a[iFrom-1].jointype & JT_OUTER)!=0 
+  if( (pSubitem->jointype & JT_OUTER)!=0 && pSub->pWhere!=0 ){
-      && pSub->pWhere!=0 ){
     return 0;
   }
 
@@ -2232,7 +2231,7 @@ static int flattenSubquery(
       pSrc->a[i+iFrom] = pSubSrc->a[i];
       memset(&pSubSrc->a[i], 0, sizeof(pSubSrc->a[i]));
     }
-    pSrc->a[iFrom+nSubSrc-1].jointype = jointype;
+    pSrc->a[iFrom].jointype = jointype;
   }
 
   /* Now begin substituting subquery result set expressions for 

src/sqliteInt.h

@@ -11,7 +11,7 @@
 *************************************************************************
 ** Internal interface definitions for SQLite.
 **
-** @(#) $Id: sqliteInt.h,v 1.530 2006/11/09 00:24:54 drh Exp $
+** @(#) $Id: sqliteInt.h,v 1.531 2006/12/16 16:25:16 drh Exp $
 */
 #ifndef _SQLITEINT_H_
 #define _SQLITEINT_H_
@@ -1617,7 +1617,9 @@ int sqlite3ArrayAllocate(void**,int,int);
 IdList *sqlite3IdListAppend(IdList*, Token*);
 int sqlite3IdListIndex(IdList*,const char*);
 SrcList *sqlite3SrcListAppend(SrcList*, Token*, Token*);
-void sqlite3SrcListAddAlias(SrcList*, Token*);
+SrcList *sqlite3SrcListAppendFromTerm(SrcList*, Token*, Token*, Token*,
+                                      Select*, Expr*, IdList*);
+void sqlite3SrcListShiftJoinType(SrcList*);
 void sqlite3SrcListAssignCursors(Parse*, SrcList*);
 void sqlite3IdListDelete(IdList*);
 void sqlite3SrcListDelete(SrcList*);

src/where.c

@@ -16,7 +16,7 @@
 ** so is applicable.  Because this module is responsible for selecting
 ** indices, you might also think of this module as the "query optimizer".
 **
-** $Id: where.c,v 1.232 2006/11/06 15:10:05 drh Exp $
+** $Id: where.c,v 1.233 2006/12/16 16:25:16 drh Exp $
 */
 #include "sqliteInt.h"
 
@@ -1854,8 +1854,7 @@ WhereInfo *sqlite3WhereBegin(
     for(j=iFrom, pTabItem=&pTabList->a[j]; j<pTabList->nSrc; j++, pTabItem++){
       int doNotReorder;  /* True if this table should not be reordered */
 
-      doNotReorder =  (pTabItem->jointype & (JT_LEFT|JT_CROSS))!=0
+      doNotReorder =  (pTabItem->jointype & (JT_LEFT|JT_CROSS))!=0;
-                   || (j>0 && (pTabItem[-1].jointype & (JT_LEFT|JT_CROSS))!=0);
       if( once && doNotReorder ) break;
       m = getMask(&maskSet, pTabItem->iCursor);
       if( (m & notReady)==0 ){
@@ -2031,7 +2030,7 @@ WhereInfo *sqlite3WhereBegin(
     ** initialize a memory cell that records if this table matches any
     ** row of the left table of the join.
     */
-    if( pLevel->iFrom>0 && (pTabItem[-1].jointype & JT_LEFT)!=0 ){
+    if( pLevel->iFrom>0 && (pTabItem[0].jointype & JT_LEFT)!=0 ){
       if( !pParse->nMem ) pParse->nMem++;
       pLevel->iLeftJoin = pParse->nMem++;
       sqlite3VdbeAddOp(v, OP_MemInt, 0, pLevel->iLeftJoin);

test/where3.test

@@ -12,7 +12,7 @@
 # focus of this file is testing the join reordering optimization
 # in cases that include a LEFT JOIN.
 #
-# $Id: where3.test,v 1.2 2006/06/06 11:45:55 drh Exp $
+# $Id: where3.test,v 1.3 2006/12/16 16:25:17 drh Exp $
 
 set testdir [file dirname $argv0]
 source $testdir/tester.tcl
@@ -78,4 +78,85 @@ do_test where3-1.2 {
   }
 } {1 {Value for C1.1} {Value for C2.1} 2 {} {Value for C2.2} 3 {Value for C1.3} {Value for C2.3}}
 
+# This procedure executes the SQL.  Then it appends 
+# the ::sqlite_query_plan variable.
+#
+proc queryplan {sql} {
+  set ::sqlite_sort_count 0
+  set data [execsql $sql]
+  return [concat $data $::sqlite_query_plan]
+}
+
+
+# If you have a from clause of the form:   A B C left join D
+# then make sure the query optimizer is able to reorder the 
+# A B C part anyway it wants. 
+#
+# Following the fix to ticket #1652, there was a time when
+# the C table would not reorder.  So the following reorderings
+# were possible:
+#
+#            A B C left join D
+#            B A C left join D
+#
+# But these reorders were not allowed
+#
+#            C A B left join D
+#            A C B left join D
+#            C B A left join D
+#            B C A left join D
+#
+# The following tests are here to verify that the latter four
+# reorderings are allowed again.
+#
+do_test where3-2.1 {
+  execsql {
+    CREATE TABLE tA(apk integer primary key, ax);
+    CREATE TABLE tB(bpk integer primary key, bx);
+    CREATE TABLE tC(cpk integer primary key, cx);
+    CREATE TABLE tD(dpk integer primary key, dx);
+  }
+  queryplan {
+    SELECT * FROM tA, tB, tC LEFT JOIN tD ON dpk=cx
+     WHERE cpk=bx AND bpk=ax
+  }
+} {tA {} tB * tC * tD *}
+do_test where3-2.2 {
+  queryplan {
+    SELECT * FROM tA, tB, tC LEFT JOIN tD ON dpk=cx
+     WHERE cpk=bx AND apk=bx
+  }
+} {tB {} tA * tC * tD *}
+do_test where3-2.3 {
+  queryplan {
+    SELECT * FROM tA, tB, tC LEFT JOIN tD ON dpk=cx
+     WHERE cpk=bx AND apk=bx
+  }
+} {tB {} tA * tC * tD *}
+do_test where3-2.4 {
+  queryplan {
+    SELECT * FROM tA, tB, tC LEFT JOIN tD ON dpk=cx
+     WHERE apk=cx AND bpk=ax
+  }
+} {tC {} tA * tB * tD *}
+do_test where3-2.5 {
+  queryplan {
+    SELECT * FROM tA, tB, tC LEFT JOIN tD ON dpk=cx
+     WHERE cpk=ax AND bpk=cx
+  }
+} {tA {} tC * tB * tD *}
+do_test where3-2.5 {
+  queryplan {
+    SELECT * FROM tA, tB, tC LEFT JOIN tD ON dpk=cx
+     WHERE bpk=cx AND apk=bx
+  }
+} {tC {} tB * tA * tD *}
+do_test where3-2.6 {
+  queryplan {
+    SELECT * FROM tA, tB, tC LEFT JOIN tD ON dpk=cx
+     WHERE cpk=bx AND apk=cx
+  }
+} {tB {} tC * tA * tD *}
+
+
 finish_test