Give the virtual table xBestIndex method access to (some) OFFSET and LIMIT

clauses.

FossilOrigin-Name: 74fa5757ee0a8499bcd6546dac1a3ecc6048ba9cff9e3e574e28e6e82e894a3d

ext/misc/qpvtab.c

@@ -103,7 +103,8 @@ static const char *azColname[] = {
   "ux",
   "rhs",
   "a", "b", "c", "d", "e",
-  "flags"
+  "flags",
+  ""
 };
 
 /*
@@ -143,6 +144,7 @@ static int qpvtabConnect(
 #define QPVTAB_D       9
 #define QPVTAB_E      10
 #define QPVTAB_FLAGS  11
+#define QPVTAB_NONE   12
   if( rc==SQLITE_OK ){
     pNew = sqlite3_malloc( sizeof(*pNew) );
     *ppVtab = (sqlite3_vtab*)pNew;
@@ -338,6 +340,7 @@ static int qpvtabBestIndex(
   for(i=0; i<pIdxInfo->nConstraint; i++){
     sqlite3_value *pVal;
     int iCol = pIdxInfo->aConstraint[i].iColumn;
+    int op = pIdxInfo->aConstraint[i].op;
     if( iCol==QPVTAB_FLAGS &&  pIdxInfo->aConstraint[i].usable ){
       pVal = 0;
       rc = sqlite3_vtab_rhs_value(pIdxInfo, i, &pVal);
@@ -347,10 +350,15 @@ static int qpvtabBestIndex(
         if( pIdxInfo->idxNum & 2 ) pIdxInfo->orderByConsumed = 1;
       }
     }
+    if( op==SQLITE_INDEX_CONSTRAINT_LIMIT
+     || op==SQLITE_INDEX_CONSTRAINT_OFFSET
+    ){
+      iCol = QPVTAB_NONE;
+    }
     sqlite3_str_appendf(pStr,"aConstraint,%d,%s,%d,%d,",
        i,
        azColname[iCol],
-       pIdxInfo->aConstraint[i].op,
+       op,
        pIdxInfo->aConstraint[i].usable);
     pVal = 0;
     rc = sqlite3_vtab_rhs_value(pIdxInfo, i, &pVal);

manifest

@@ -1,5 +1,5 @@
-C Enforce\sthe\srestriction\sthat\s'unixepoch'\sonly\sworks\sas\sthe\sfirst\smodifier\nafter\sthe\stime-value.\s\sThis\shas\sbeen\sdocumented\ssince\s2004,\sbut\shas\snever\nactually\sbeen\senforced\sbefore.\s\sAlso\sadd\snew\stest\scases\sfor\sdate/time\nfunctions\swith\sevidence\smarks.
+C Give\sthe\svirtual\stable\sxBestIndex\smethod\saccess\sto\s(some)\sOFFSET\sand\sLIMIT\nclauses.
-D 2022-01-27T13:52:01.555
+D 2022-01-27T16:14:50.962
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -316,7 +316,7 @@ F ext/misc/noop.c 81efe4cad9ec740e64388b14281cb983e6e2c223fed43eb77ab3e34946e0c1
 F ext/misc/normalize.c bd84355c118e297522aba74de34a4fd286fc775524e0499b14473918d09ea61f
 F ext/misc/percentile.c b9086e223d583bdaf8cb73c98a6539d501a2fc4282654adbfea576453d82e691
 F ext/misc/prefixes.c 0f4f8cff5aebc00a7e3ac4021fd59cfe1a8e17c800ceaf592859ecb9cbc38196
-F ext/misc/qpvtab.c c662fa0a452ad286e49b6c83ac917600656b2eb47d2225ff6185c56bf80cf8d2
+F ext/misc/qpvtab.c 03986dca441274933dd924170ceee50ad248d24a4cd6a686ff45d5e65e5deac4
 F ext/misc/regexp.c b267fd05ff8d38b22f4c2809d7b7a2c61d522e9faf2feb928dbb9662e4a3a386
 F ext/misc/remember.c add730f0f7e7436cd15ea3fd6a90fd83c3f706ab44169f7f048438b7d6baa69c
 F ext/misc/rot13.c 51ac5f51e9d5fd811db58a9c23c628ad5f333c173f1fc53c8491a3603d38556c
@@ -502,10 +502,10 @@ F src/ctime.c 2cce39df1a13e05b7633e6d21b651f21492471f991dd7b323a4ee4e7b7f0b7f1
 F src/date.c 41627dec396f3d33e2c317a065f9d59bb535982b2ea3a561c96e4d4cf1137b65
 F src/dbpage.c 8a01e865bf8bc6d7b1844b4314443a6436c07c3efe1d488ed89e81719047833a
 F src/dbstat.c 861e08690fcb0f2ee1165eff0060ea8d4f3e2ea10f80dab7d32ad70443a6ff2d
-F src/delete.c 52897a8516dc40753503c25eed0e305f09cc50ae474f22b0b4fd31d3b879cc08
+F src/delete.c b5f1716b4d723db48254ee0f896e362cd029e865e05414139ea7f539f3884e1d
 F src/expr.c 9658bccd1598211ace848c8ca9480dbf8be08dfee1db5cf03897b34b7b6e8fef
 F src/fault.c 460f3e55994363812d9d60844b2a6de88826e007
-F src/fkey.c 5b73f7a7c00f06017531a5bd258cbc2c7a294e55a7f84a729fe27aa525242560
+F src/fkey.c 06e4ac33031b02dde7130c12e79cddf4dc5cfa72b23d8e63a3c26878fc9c1d3c
 F src/func.c 8fddc42bce95d17938252a543f86fe29e479366e80fbd112a1822913b6247776
 F src/global.c 1f56aead86e8a18c4415638f5e6c4d0a0550427f4b3f5d065ba5164cc09c22e8
 F src/hash.c 8d7dda241d0ebdafb6ffdeda3149a412d7df75102cecfc1021c98d6219823b19
@@ -552,12 +552,12 @@ F src/printf.c 975f1f5417f2526365b6e6d7f22332e3e11806dad844701d92846292b654ba9a
 F src/random.c 097dc8b31b8fba5a9aca1697aeb9fd82078ec91be734c16bffda620ced7ab83c
 F src/resolve.c 24032ae57aec10df2f3fa2e20be0aae7d256bc704124b76c52d763440c7c0fe9
 F src/rowset.c ba9515a922af32abe1f7d39406b9d35730ed65efab9443dc5702693b60854c92
-F src/select.c 5799f5b15e27bcb8262caec7821f3ef89575e539237db3141be0d26cf8efd22c
+F src/select.c a6d2d4bed279d7fe4fcedaf297eaf6441e8e17c6e3947a32d24d23be52ac02f2
 F src/shell.c.in e80a140e92e342e2f92d405a77155c8e3a67c9b1d0bdbacb92885960cd4fc8f2
-F src/sqlite.h.in 31c2c8d737814369bd3b71f3849c4a97ef7ede0aa3ce976ecb11632fa5f1f863
+F src/sqlite.h.in da0e94f140f3f054f0eca8fc4a183167bedc7ae9c51822390c62369455eae5f8
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
 F src/sqlite3ext.h 5d54cf13d3406d8eb65d921a0d3c349de6126b732e695e79ecd4830ce86b4f8a
-F src/sqliteInt.h 33fbafb55b48f63b791c563378345ebdbbcb73e8fd63a1c22e4df05f435d4714
+F src/sqliteInt.h 8ef2996e02476f73e41ba977f819bda0cc68b7ce238cf404b9b8930df57bc1d0
 F src/sqliteLimit.h d7323ffea5208c6af2734574bae933ca8ed2ab728083caa117c9738581a31657
 F src/status.c 4b8bc2a6905163a38b739854a35b826c737333fab5b1f8e03fa7eb9a4799c4c1
 F src/table.c 0f141b58a16de7e2fbe81c308379e7279f4c6b50eb08efeec5892794a0ba30d1
@@ -574,7 +574,7 @@ F src/test9.c 12e5ba554d2d1cbe0158f6ab3f7ffcd7a86ee4e5
 F src/test_async.c 195ab49da082053fdb0f949c114b806a49ca770a
 F src/test_autoext.c 915d245e736652a219a907909bb6710f0d587871
 F src/test_backup.c bf5da90c9926df0a4b941f2d92825a01bbe090a0
-F src/test_bestindex.c 78809f11026f18a93fcfd798d9479cba37e1201c830260bf1edc674b2fa9b857
+F src/test_bestindex.c ba0314d3bca8b00fa0daaf113a314986f73ea8ad85a7562f983638d09a29045c
 F src/test_blob.c ae4a0620b478548afb67963095a7417cd06a4ec0a56adb453542203bfdcb31ce
 F src/test_btree.c 8b2dc8b8848cf3a4db93f11578f075e82252a274
 F src/test_config.c 284c29912736f68b0a583a920bf63fd8f9125dffb8a75cb0676e58502b2f7908
@@ -619,7 +619,7 @@ F src/threads.c 4ae07fa022a3dc7c5beb373cf744a85d3c5c6c3c
 F src/tokenize.c b74d878aa7c82ec8460779468061a96185e22257f68ab785b69abce354b70446
 F src/treeview.c 9dfdb7ff7f6645d0a6458dbdf4ffac041c071c4533a6db8bb6e502b979ac67bc
 F src/trigger.c 692972e4393dfc8017a1a527c1ea1b96ce3d101e84584cd832fcfb83d22b50b2
-F src/update.c 7dfa3866cdfb28bf952c38054c1722720d8ff64750dea421790aecc91f640516
+F src/update.c f875b0d59da5c3055a0b2ac20560e1650229c6787e78de5e9836267b5cbb8359
 F src/upsert.c 8789047a8f0a601ea42fa0256d1ba3190c13746b6ba940fe2d25643a7e991937
 F src/utf.c ee39565f0843775cc2c81135751ddd93eceb91a673ea2c57f61c76f288b041a0
 F src/util.c 602fe229f32a96ceccae4f40824129669582096f7c355f53dbac156c9fecef23
@@ -639,10 +639,10 @@ F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
 F src/wal.c b9df133a705093da8977da5eb202eaadb844839f1c7297c08d33471f5491843d
 F src/wal.h c3aa7825bfa2fe0d85bef2db94655f99870a285778baa36307c0a16da32b226a
 F src/walker.c f890a3298418d7cba3b69b8803594fdc484ea241206a8dfa99db6dd36f8cbb3b
-F src/where.c a14990c7b35e95f8f9cb0dc0d6d2e32fa99135a716a04027cefa48138d280ecb
+F src/where.c f89c21296cdf23bbc73333c77a01e0bfdccc9d1a767d38a145e3a8658456b66c
-F src/whereInt.h 8a215acde0f833a4dea3d30a7bbed9f48b4b547b5d5e34cd02acee366476ab80
+F src/whereInt.h e23780eb06810dc8bd7d855c97a667bf116cb929d8aa107ce1db91df8e47aaa8
-F src/wherecode.c 8da0f873278ed6aad42bf2028404d7178dd9cfcdc7179ecc61a87591a15a07d2
+F src/wherecode.c 37878a0a6f790b77f41e7b3d77c42f14bded09aef3d363eaf19b3ee02e765666
-F src/whereexpr.c 9f64c39e53070584e99e4d20c1dd3397e125fabbae8fd414ffec574c410ac7d3
+F src/whereexpr.c 50b09b3583301d0a5aef0e5b5d225f4d2b0eba2e36e3f9d0b914e110d4b2f6ce
 F src/window.c dfaec4abc6012cbc18e4a202ca3a5d5a0efcc4011d86a06d882ddaab8aedee4d
 F test/8_3_names.test ebbb5cd36741350040fd28b432ceadf495be25b2
 F test/affinity2.test ce1aafc86e110685b324e9a763eab4f2a73f737842ec3b687bd965867de90627
@@ -1942,8 +1942,11 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P a8db69411b0d1275909adeb21027784ada17af24efe3a59ae0ae2a897659ff17
+P 64fa9e8c87179211cec248e6dfd7578502e6e969a19e91a4f0e21ed9b972a6bc
-R a92b0ae1c265a80dc4f7e5c12c916bf4
+R c3554501c3177117c353a66ed5c4eb7c
+T *branch * vtab-limit-offset
+T *sym-vtab-limit-offset *
+T -sym-trunk *
 U drh
-Z 47b9e1bb1e6a61a53486ee72f7ca6190
+Z 853246eb39d3c5347b902f7c653bc6b9
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-64fa9e8c87179211cec248e6dfd7578502e6e969a19e91a4f0e21ed9b972a6bc
+74fa5757ee0a8499bcd6546dac1a3ecc6048ba9cff9e3e574e28e6e82e894a3d

src/delete.c

@@ -478,7 +478,7 @@ void sqlite3DeleteFrom(
     **  ONEPASS_SINGLE: One-pass approach - at most one row deleted.
     **  ONEPASS_MULTI:  One-pass approach - any number of rows may be deleted.
     */
-    pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, 0, 0, wcf, iTabCur+1);
+    pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, 0, 0,0,wcf,iTabCur+1);
     if( pWInfo==0 ) goto delete_from_cleanup;
     eOnePass = sqlite3WhereOkOnePass(pWInfo, aiCurOnePass);
     assert( IsVirtual(pTab)==0 || eOnePass!=ONEPASS_MULTI );

src/fkey.c

@@ -651,7 +651,7 @@ static void fkScanChildren(
   ** clause. For each row found, increment either the deferred or immediate
   ** foreign key constraint counter. */
   if( pParse->nErr==0 ){
-    pWInfo = sqlite3WhereBegin(pParse, pSrc, pWhere, 0, 0, 0, 0);
+    pWInfo = sqlite3WhereBegin(pParse, pSrc, pWhere, 0, 0, 0, 0, 0);
     sqlite3VdbeAddOp2(v, OP_FkCounter, pFKey->isDeferred, nIncr);
     if( pWInfo ){
       sqlite3WhereEnd(pWInfo);

src/select.c

@@ -6898,7 +6898,7 @@ int sqlite3Select(
     /* Begin the database scan. */
     SELECTTRACE(1,pParse,p,("WhereBegin\n"));
     pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, sSort.pOrderBy,
-                               p->pEList, wctrlFlags, p->nSelectRow);
+                               p->pEList, p, wctrlFlags, p->nSelectRow);
     if( pWInfo==0 ) goto select_end;
     if( sqlite3WhereOutputRowCount(pWInfo) < p->nSelectRow ){
       p->nSelectRow = sqlite3WhereOutputRowCount(pWInfo);
@@ -7162,7 +7162,7 @@ int sqlite3Select(
       sqlite3VdbeAddOp2(v, OP_Gosub, regReset, addrReset);
       SELECTTRACE(1,pParse,p,("WhereBegin\n"));
       pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, pGroupBy, pDistinct,
-          WHERE_GROUPBY | (orderByGrp ? WHERE_SORTBYGROUP : 0) | distFlag, 0
+          0, (WHERE_GROUPBY|(orderByGrp ? WHERE_SORTBYGROUP : 0)|distFlag), 0
       );
       if( pWInfo==0 ){
         sqlite3ExprListDelete(db, pDistinct);
@@ -7460,7 +7460,7 @@ int sqlite3Select(
 
         SELECTTRACE(1,pParse,p,("WhereBegin\n"));
         pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, pMinMaxOrderBy,
-                                   pDistinct, minMaxFlag|distFlag, 0);
+                                   pDistinct, 0, minMaxFlag|distFlag, 0);
         if( pWInfo==0 ){
           goto select_end;
         }

src/sqlite.h.in

@@ -7148,6 +7148,8 @@ struct sqlite3_index_info {
 #define SQLITE_INDEX_CONSTRAINT_ISNOTNULL 70
 #define SQLITE_INDEX_CONSTRAINT_ISNULL    71
 #define SQLITE_INDEX_CONSTRAINT_IS        72
+#define SQLITE_INDEX_CONSTRAINT_LIMIT     73
+#define SQLITE_INDEX_CONSTRAINT_OFFSET    74
 #define SQLITE_INDEX_CONSTRAINT_FUNCTION 150
 
 /*

src/sqliteInt.h

@@ -4577,7 +4577,8 @@ void sqlite3CodeChangeCount(Vdbe*,int,const char*);
 void sqlite3DeleteFrom(Parse*, SrcList*, Expr*, ExprList*, Expr*);
 void sqlite3Update(Parse*, SrcList*, ExprList*,Expr*,int,ExprList*,Expr*,
                    Upsert*);
-WhereInfo *sqlite3WhereBegin(Parse*,SrcList*,Expr*,ExprList*,ExprList*,u16,int);
+WhereInfo *sqlite3WhereBegin(Parse*,SrcList*,Expr*,ExprList*,
+                             ExprList*,Select*,u16,int);
 void sqlite3WhereEnd(WhereInfo*);
 LogEst sqlite3WhereOutputRowCount(WhereInfo*);
 int sqlite3WhereIsDistinct(WhereInfo*);

src/test_bestindex.c

@@ -424,6 +424,10 @@ static int tclBestIndex(sqlite3_vtab *tab, sqlite3_index_info *pIdxInfo){
         zOp = "isnull"; break;
       case SQLITE_INDEX_CONSTRAINT_IS:
         zOp = "is"; break;
+      case SQLITE_INDEX_CONSTRAINT_LIMIT:
+        zOp = "limit"; break;
+      case SQLITE_INDEX_CONSTRAINT_OFFSET:
+        zOp = "offset"; break;
     }
 
     Tcl_ListObjAppendElement(0, pElem, Tcl_NewStringObj("op", -1));

src/update.c

@@ -723,7 +723,7 @@ void sqlite3Update(
       if( !pParse->nested && !pTrigger && !hasFK && !chngKey && !bReplace ){
         flags |= WHERE_ONEPASS_MULTIROW;
       }
-      pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, 0, 0, flags,iIdxCur);
+      pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere,0,0,0,flags,iIdxCur);
       if( pWInfo==0 ) goto update_cleanup;
 
       /* A one-pass strategy that might update more than one row may not
@@ -1245,7 +1245,9 @@ static void updateVirtualTable(
     regRowid = ++pParse->nMem;
 
     /* Start scanning the virtual table */
-    pWInfo = sqlite3WhereBegin(pParse, pSrc,pWhere,0,0,WHERE_ONEPASS_DESIRED,0);
+    pWInfo = sqlite3WhereBegin(
+        pParse, pSrc, pWhere, 0, 0, 0, WHERE_ONEPASS_DESIRED, 0
+    );
     if( pWInfo==0 ) return;
 
     /* Populate the argument registers. */

src/where.c

@@ -3459,6 +3459,16 @@ static int whereLoopAddBtree(
 
 #ifndef SQLITE_OMIT_VIRTUALTABLE
 
+/*
+** Return true if pTerm is a virtual table LIMIT or OFFSET term.
+*/
+static int isLimitTerm(WhereTerm *pTerm){
+  return pTerm->eOperator==WO_AUX && (
+       pTerm->eMatchOp==SQLITE_INDEX_CONSTRAINT_LIMIT 
+    || pTerm->eMatchOp==SQLITE_INDEX_CONSTRAINT_OFFSET
+  );
+}
+
 /*
 ** Argument pIdxInfo is already populated with all constraints that may
 ** be used by the virtual table identified by pBuilder->pNew->iTab. This
@@ -3486,7 +3496,8 @@ static int whereLoopAddVirtualOne(
   u16 mExclude,                   /* Exclude terms using these operators */
   sqlite3_index_info *pIdxInfo,   /* Populated object for xBestIndex */
   u16 mNoOmit,                    /* Do not omit these constraints */
-  int *pbIn                       /* OUT: True if plan uses an IN(...) op */
+  int *pbIn,                      /* OUT: True if plan uses an IN(...) op */
+  int *pbRetryLimit               /* OUT: Retry without LIMIT/OFFSET */
 ){
   WhereClause *pWC = pBuilder->pWC;
   struct sqlite3_index_constraint *pIdxCons;
@@ -3511,6 +3522,7 @@ static int whereLoopAddVirtualOne(
     pIdxCons->usable = 0;
     if( (pTerm->prereqRight & mUsable)==pTerm->prereqRight 
      && (pTerm->eOperator & mExclude)==0
+     && (pbRetryLimit || !isLimitTerm(pTerm))
     ){
       pIdxCons->usable = 1;
     }
@@ -3589,6 +3601,21 @@ static int whereLoopAddVirtualOne(
         pIdxInfo->idxFlags &= ~SQLITE_INDEX_SCAN_UNIQUE;
         *pbIn = 1; assert( (mExclude & WO_IN)==0 );
       }
+
+      if( isLimitTerm(pTerm) && *pbIn ){
+        /* If there is an IN(...) term handled as an == (separate call to
+        ** xFilter for each value on the RHS of the IN) and a LIMIT or
+        ** OFFSET term handled as well, the plan is unusable. Set output
+        ** variable *pbRetryLimit to true to tell the caller to retry with
+        ** LIMIT and OFFSET disabled. */
+        if( pIdxInfo->needToFreeIdxStr ){
+          sqlite3_free(pIdxInfo->idxStr);
+          pIdxInfo->idxStr = 0;
+          pIdxInfo->needToFreeIdxStr = 0;
+        }
+        *pbRetryLimit = 1;
+        return SQLITE_OK;
+      }
     }
   }
 
@@ -3751,6 +3778,7 @@ static int whereLoopAddVirtual(
   WhereLoop *pNew;
   Bitmask mBest;               /* Tables used by best possible plan */
   u16 mNoOmit;
+  int bRetry = 0;              /* True to retry with LIMIT/OFFSET disabled */
 
   assert( (mPrereq & mUnusable)==0 );
   pWInfo = pBuilder->pWInfo;
@@ -3774,7 +3802,15 @@ static int whereLoopAddVirtual(
   /* First call xBestIndex() with all constraints usable. */
   WHERETRACE(0x800, ("BEGIN %s.addVirtual()\n", pSrc->pTab->zName));
   WHERETRACE(0x40, ("  VirtualOne: all usable\n"));
-  rc = whereLoopAddVirtualOne(pBuilder, mPrereq, ALLBITS, 0, p, mNoOmit, &bIn);
+  rc = whereLoopAddVirtualOne(
+      pBuilder, mPrereq, ALLBITS, 0, p, mNoOmit, &bIn, &bRetry
+  );
+  if( bRetry ){
+    assert( rc==SQLITE_OK );
+    rc = whereLoopAddVirtualOne(
+        pBuilder, mPrereq, ALLBITS, 0, p, mNoOmit, &bIn, 0
+    );
+  }
 
   /* If the call to xBestIndex() with all terms enabled produced a plan
   ** that does not require any source tables (IOW: a plan with mBest==0)
@@ -3792,7 +3828,7 @@ static int whereLoopAddVirtual(
     if( bIn ){
       WHERETRACE(0x40, ("  VirtualOne: all usable w/o IN\n"));
       rc = whereLoopAddVirtualOne(
-          pBuilder, mPrereq, ALLBITS, WO_IN, p, mNoOmit, &bIn);
+          pBuilder, mPrereq, ALLBITS, WO_IN, p, mNoOmit, &bIn, 0);
       assert( bIn==0 );
       mBestNoIn = pNew->prereq & ~mPrereq;
       if( mBestNoIn==0 ){
@@ -3819,7 +3855,7 @@ static int whereLoopAddVirtual(
       WHERETRACE(0x40, ("  VirtualOne: mPrev=%04llx mNext=%04llx\n",
                        (sqlite3_uint64)mPrev, (sqlite3_uint64)mNext));
       rc = whereLoopAddVirtualOne(
-          pBuilder, mPrereq, mNext|mPrereq, 0, p, mNoOmit, &bIn);
+          pBuilder, mPrereq, mNext|mPrereq, 0, p, mNoOmit, &bIn, 0);
       if( pNew->prereq==mPrereq ){
         seenZero = 1;
         if( bIn==0 ) seenZeroNoIN = 1;
@@ -3832,7 +3868,7 @@ static int whereLoopAddVirtual(
     if( rc==SQLITE_OK && seenZero==0 ){
       WHERETRACE(0x40, ("  VirtualOne: all disabled\n"));
       rc = whereLoopAddVirtualOne(
-          pBuilder, mPrereq, mPrereq, 0, p, mNoOmit, &bIn);
+          pBuilder, mPrereq, mPrereq, 0, p, mNoOmit, &bIn, 0);
       if( bIn==0 ) seenZeroNoIN = 1;
     }
 
@@ -3842,7 +3878,7 @@ static int whereLoopAddVirtual(
     if( rc==SQLITE_OK && seenZeroNoIN==0 ){
       WHERETRACE(0x40, ("  VirtualOne: all disabled and w/o IN\n"));
       rc = whereLoopAddVirtualOne(
-          pBuilder, mPrereq, mPrereq, WO_IN, p, mNoOmit, &bIn);
+          pBuilder, mPrereq, mPrereq, WO_IN, p, mNoOmit, &bIn, 0);
     }
   }
 
@@ -5248,6 +5284,7 @@ WhereInfo *sqlite3WhereBegin(
   Expr *pWhere,           /* The WHERE clause */
   ExprList *pOrderBy,     /* An ORDER BY (or GROUP BY) clause, or NULL */
   ExprList *pResultSet,   /* Query result set.  Req'd for DISTINCT */
+  Select *pLimit,         /* Use this LIMIT/OFFSET clause, if any */
   u16 wctrlFlags,         /* The WHERE_* flags defined in sqliteInt.h */
   int iAuxArg             /* If WHERE_OR_SUBCLAUSE is set, index cursor number
                           ** If WHERE_USE_LIMIT, then the limit amount */
@@ -5324,6 +5361,9 @@ WhereInfo *sqlite3WhereBegin(
   pWInfo->wctrlFlags = wctrlFlags;
   pWInfo->iLimit = iAuxArg;
   pWInfo->savedNQueryLoop = pParse->nQueryLoop;
+#ifndef SQLITE_OMIT_VIRTUALTABLE
+  pWInfo->pLimit = pLimit;
+#endif
   memset(&pWInfo->nOBSat, 0, 
          offsetof(WhereInfo,sWC) - offsetof(WhereInfo,nOBSat));
   memset(&pWInfo->a[0], 0, sizeof(WhereLoop)+nTabList*sizeof(WhereLevel));
@@ -5392,6 +5432,7 @@ WhereInfo *sqlite3WhereBegin(
   
   /* Analyze all of the subexpressions. */
   sqlite3WhereExprAnalyze(pTabList, &pWInfo->sWC);
+  sqlite3WhereAddLimit(&pWInfo->sWC, pLimit);
   if( db->mallocFailed ) goto whereBeginError;
 
   /* Special case: WHERE terms that do not refer to any tables in the join

src/whereInt.h

@@ -453,6 +453,9 @@ struct WhereInfo {
   ExprList *pOrderBy;       /* The ORDER BY clause or NULL */
   ExprList *pResultSet;     /* Result set of the query */
   Expr *pWhere;             /* The complete WHERE clause */
+#ifndef SQLITE_OMIT_VIRTUALTABLE
+  Select *pLimit;           /* Used to access LIMIT expr/registers for vtabs */
+#endif
   int aiCurOnePass[2];      /* OP_OpenWrite cursors for the ONEPASS opt */
   int iContinue;            /* Jump here to continue with next record */
   int iBreak;               /* Jump here to break out of the loop */
@@ -538,6 +541,7 @@ Bitmask sqlite3WhereCodeOneLoopStart(
 void sqlite3WhereClauseInit(WhereClause*,WhereInfo*);
 void sqlite3WhereClauseClear(WhereClause*);
 void sqlite3WhereSplit(WhereClause*,Expr*,u8);
+void sqlite3WhereAddLimit(WhereClause*, Select*);
 Bitmask sqlite3WhereExprUsage(WhereMaskSet*, Expr*);
 Bitmask sqlite3WhereExprUsageNN(WhereMaskSet*, Expr*);
 Bitmask sqlite3WhereExprListUsage(WhereMaskSet*, ExprList*);

src/wherecode.c

@@ -2358,7 +2358,7 @@ Bitmask sqlite3WhereCodeOneLoopStart(
         /* Loop through table entries that match term pOrTerm. */
         ExplainQueryPlan((pParse, 1, "INDEX %d", ii+1));
         WHERETRACE(0xffff, ("Subplan for OR-clause:\n"));
-        pSubWInfo = sqlite3WhereBegin(pParse, pOrTab, pOrExpr, 0, 0,
+        pSubWInfo = sqlite3WhereBegin(pParse, pOrTab, pOrExpr, 0, 0, 0,
                                       WHERE_OR_SUBCLAUSE, iCovCur);
         assert( pSubWInfo || pParse->nErr );
         if( pSubWInfo ){

src/whereexpr.c

@@ -1522,6 +1522,80 @@ void sqlite3WhereSplit(WhereClause *pWC, Expr *pExpr, u8 op){
   }
 }
 
+/*
+** Add either a LIMIT (if eMatchOp==SQLITE_INDEX_CONSTRAINT_LIMIT) or 
+** OFFSET (if eMatchOp==SQLITE_INDEX_CONSTRAINT_OFFSET) term to the 
+** where-clause passed as the first argument. The value for the term
+** is found in register iReg.
+*/
+void whereAddLimitExpr(WhereClause *pWC, int iReg, int iCsr, int eMatchOp){
+  Parse *pParse = pWC->pWInfo->pParse;
+  sqlite3 *db = pParse->db;
+  Expr *pExpr;
+
+  pExpr = sqlite3PExpr(pParse, TK_MATCH, 0, sqlite3Expr(db,TK_REGISTER,0));
+  if( pExpr ){
+    WhereTerm *pTerm;
+    int idx;
+    pExpr->pRight->iTable = iReg;
+    idx = whereClauseInsert(pWC, pExpr, TERM_DYNAMIC|TERM_VIRTUAL);
+    pTerm = &pWC->a[idx];
+    pTerm->leftCursor = iCsr;
+    pTerm->eOperator = WO_AUX;
+    pTerm->eMatchOp = eMatchOp;
+  }
+}
+
+/*
+** Possibly add terms corresponding to the LIMIT and OFFSET clauses of the
+** SELECT statement passed as the second argument. These terms are only
+** added if:
+**
+**   1. The SELECT statement has a LIMIT clause, and
+**   2. The SELECT statement is not an aggregate or DISTINCT query, and
+**   3. The SELECT statement has exactly one object in its from clause, and
+**      that object is a virtual table, and
+**   4. There are no terms in the WHERE clause that will not be passed
+**      to the virtual table xBestIndex method.
+**   5. The ORDER BY clause, if any, will be made available to the xBestIndex
+**      method.
+**
+** LIMIT and OFFSET terms are ignored by most of the planner code. They
+** exist only so that they may be passed to the xBestIndex method of the
+** single virtual table in the FROM clause of the SELECT.
+*/
+void sqlite3WhereAddLimit(WhereClause *pWC, Select *p){
+  assert( p==0 || (p->pGroupBy==0 && (p->selFlags & SF_Aggregate)==0) );
+  if( (p && p->pLimit)                                          /* 1 */
+   && (p->selFlags & (SF_Distinct|SF_Aggregate))==0             /* 2 */
+   && (p->pSrc->nSrc==1 && IsVirtual(p->pSrc->a[0].pTab))       /* 3 */
+  ){
+    ExprList *pOrderBy = p->pOrderBy;
+    int iCsr = p->pSrc->a[0].iCursor;
+    int ii;
+
+    /* Check condition (4). Return early if it is not met. */
+    for(ii=0; ii<pWC->nTerm; ii++){
+      if( pWC->a[ii].leftCursor!=iCsr ) return;
+    }
+
+    /* Check condition (5). Return early if it is not met. */
+    if( pOrderBy ){
+      for(ii=0; ii<pOrderBy->nExpr; ii++){
+        Expr *pExpr = pOrderBy->a[ii].pExpr;
+        if( pExpr->op!=TK_COLUMN || pExpr->iTable!=iCsr ) return;
+        if( pOrderBy->a[ii].sortFlags & KEYINFO_ORDER_BIGNULL ) return;
+      }
+    }
+
+    /* All conditions are met. Add the terms to the where-clause object. */
+    whereAddLimitExpr(pWC, p->iLimit, iCsr, SQLITE_INDEX_CONSTRAINT_LIMIT);
+    if( p->iOffset>0 ){
+      whereAddLimitExpr(pWC, p->iOffset, iCsr, SQLITE_INDEX_CONSTRAINT_OFFSET);
+    }
+  }
+}
+
 /*
 ** Initialize a preallocated WhereClause structure.
 */