Use transitivity to move constraints into the outer loops of a join whenever

possible, thereby reducing the amount of work that needs to occur in
inner loops.

FossilOrigin-Name: 5f4907e1c6230e3dd904bd99e1c48c576c669f63

manifest

@@ -1,5 +1,5 @@
-C Add\sthe\s"warning"\scommand\sto\sthe\sTCL\stest\sinfrastructure.\s\sFix\sproblems\nwith\sthe\sloadext.test\smodule.
-D 2013-04-19T12:32:52.666
+C Use\stransitivity\sto\smove\sconstraints\sinto\sthe\souter\sloops\sof\sa\sjoin\swhenever\npossible,\sthereby\sreducing\sthe\samount\sof\swork\sthat\sneeds\sto\soccur\sin\ninner\sloops.
+D 2013-04-22T02:39:10.341
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 3dd3fcb87b70c78d99b2c8a03e44ec86d6ca9ce2
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -258,7 +258,7 @@ F src/vtab.c b05e5f1f4902461ba9f5fc49bb7eb7c3a0741a83
 F src/wal.c 436bfceb141b9423c45119e68e444358ee0ed35d
 F src/wal.h a4d3da523d55a226a0b28e9058ef88d0a8051887
 F src/walker.c 3d75ba73de15e0f8cd0737643badbeb0e002f07b
-F src/where.c e63f84e5583133c77573b78d3696dccd97bfd00d
+F src/where.c c7c74fe8e354b60dee0810ea8b954c5ccb9e0f3c
 F test/8_3_names.test 631ea964a3edb091cf73c3b540f6bcfdb36ce823
 F test/aggerror.test a867e273ef9e3d7919f03ef4f0e8c0d2767944f2
 F test/aggnested.test 45c0201e28045ad38a530b5a144b73cd4aa2cfd6
@@ -1051,7 +1051,7 @@ F tool/vdbe-compress.tcl f12c884766bd14277f4fcedcae07078011717381
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh fbc018d67fd7395f440c28f33ef0f94420226381
 F tool/win/sqlite.vsix 97894c2790eda7b5bce3cc79cb2a8ec2fde9b3ac
-P a85b6ecefa14fcfe6ebfceabf910f00c3721be7d
-R 2c3aca07297ff95a6b74db849941a18d
+P 514adbbd8cf3e296f55e8f803bddaac8ad8b2c96
+R a81fa97db156009318d49bf4c6dae35e
 U drh
-Z bfc695f8f3325c7943f46501f9086d37
+Z 1c3c5b72018db605301d161eada3f156

manifest.uuid

@@ -1 +1 @@
-514adbbd8cf3e296f55e8f803bddaac8ad8b2c96
+5f4907e1c6230e3dd904bd99e1c48c576c669f63

src/where.c

@@ -4161,6 +4161,7 @@ static Bitmask codeOneLoopStart(
   int addrCont;                   /* Jump here to continue with next cycle */
   int iRowidReg = 0;        /* Rowid is stored in this register, if not zero */
   int iReleaseReg = 0;      /* Temp register to free before returning */
+  Bitmask newNotReady;      /* Return value */
 
   pParse = pWInfo->pParse;
   v = pParse->pVdbe;
@@ -4171,6 +4172,7 @@ static Bitmask codeOneLoopStart(
   bRev = (pLevel->plan.wsFlags & WHERE_REVERSE)!=0;
   omitTable = (pLevel->plan.wsFlags & WHERE_IDX_ONLY)!=0 
            && (wctrlFlags & WHERE_FORCE_TABLE)==0;
+  VdbeNoopComment((v, "Begin Join Loop %d", iLevel));
 
   /* Create labels for the "break" and "continue" instructions
   ** for the current loop.  Jump to addrBrk to break out of a loop.
@@ -4821,7 +4823,7 @@ static Bitmask codeOneLoopStart(
     pLevel->p2 = 1 + sqlite3VdbeAddOp2(v, aStart[bRev], iCur, addrBrk);
     pLevel->p5 = SQLITE_STMTSTATUS_FULLSCAN_STEP;
   }
-  notReady &= ~getMask(pWC->pMaskSet, iCur);
+  newNotReady = notReady & ~getMask(pWC->pMaskSet, iCur);
 
   /* Insert code to test every subexpression that can be completely
   ** computed using the current set of tables.
@@ -4835,7 +4837,7 @@ static Bitmask codeOneLoopStart(
     testcase( pTerm->wtFlags & TERM_VIRTUAL ); /* IMP: R-30575-11662 */
     testcase( pTerm->wtFlags & TERM_CODED );
     if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_CODED) ) continue;
-    if( (pTerm->prereqAll & notReady)!=0 ){
+    if( (pTerm->prereqAll & newNotReady)!=0 ){
       testcase( pWInfo->untestedTerms==0
                && (pWInfo->wctrlFlags & WHERE_ONETABLE_ONLY)!=0 );
       pWInfo->untestedTerms = 1;
@@ -4850,6 +4852,32 @@ static Bitmask codeOneLoopStart(
     pTerm->wtFlags |= TERM_CODED;
   }
 
+  /* Insert code to test for implied constraints based on transitivity
+  ** of the "==" operator.
+  **
+  ** Example: If the WHERE clause contains "t1.a=t2.b" and "t2.b=123"
+  ** and we are coding the t1 loop and the t2 loop has not yet coded,
+  ** then we cannot use the "t1.a=t2.b" constraint, but we can code
+  ** the implied "t1.a=123" constraint.
+  */
+  for(pTerm=pWC->a, j=pWC->nTerm; j>0; j--, pTerm++){
+    Expr *pE;
+    WhereTerm *pAlt;
+    Expr sEq;
+    if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_CODED) ) continue;
+    if( pTerm->eOperator!=(WO_EQUIV|WO_EQ) ) continue;
+    if( pTerm->leftCursor!=iCur ) continue;
+    pE = pTerm->pExpr;
+    assert( !ExprHasProperty(pE, EP_FromJoin) );
+    assert( (pTerm->prereqRight & newNotReady)!=0 );
+    pAlt = findTerm(pWC, iCur, pTerm->u.leftColumn, notReady, WO_EQ|WO_IN, 0);
+    if( pAlt==0 ) continue;
+    VdbeNoopComment((v, "begin transitive constraint"));
+    sEq = *pAlt->pExpr;
+    sEq.pLeft = pE->pLeft;
+    sqlite3ExprIfFalse(pParse, &sEq, addrCont, SQLITE_JUMPIFNULL);
+  }
+
   /* For a LEFT OUTER JOIN, generate code that will record the fact that
   ** at least one row of the right table has matched the left table.  
   */
@@ -4862,7 +4890,7 @@ static Bitmask codeOneLoopStart(
       testcase( pTerm->wtFlags & TERM_VIRTUAL );  /* IMP: R-30575-11662 */
       testcase( pTerm->wtFlags & TERM_CODED );
       if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_CODED) ) continue;
-      if( (pTerm->prereqAll & notReady)!=0 ){
+      if( (pTerm->prereqAll & newNotReady)!=0 ){
         assert( pWInfo->untestedTerms );
         continue;
       }
@@ -4873,7 +4901,7 @@ static Bitmask codeOneLoopStart(
   }
   sqlite3ReleaseTempReg(pParse, iReleaseReg);
 
-  return notReady;
+  return newNotReady;
 }
 
 #if defined(SQLITE_TEST)