Only run the OP_OpenRead opcodes for a correlated subquery once, on the initial

iteration. Keep the cursor open for subsequent runs. This was suppose to be a
performance enhancement, but it is difficult to come up with a query where
is makes a significant difference.  Hence, the change is getting parked
in a branch.

FossilOrigin-Name: 3ad687b7aa908b0e914be48cc8a21af5d07e52d9

manifest

@@ -1,5 +1,5 @@
-C In\sthe\scommand-line\sshell\sfor\sCSV\simport,\sif\sthe\slines\sare\s\\r\\n\sterminated\nand\sthe\slast\sfield\sis\sblank,\smake\ssure\san\sempty\sstring\sand\snot\sa\s"\\r"\sstring\nis\simported.
-D 2014-02-26T13:53:34.384
+C Only\srun\sthe\sOP_OpenRead\sopcodes\sfor\sa\scorrelated\ssubquery\sonce,\son\sthe\sinitial\niteration.\sKeep\sthe\scursor\sopen\sfor\ssubsequent\sruns.\sThis\swas\ssuppose\sto\sbe\sa\nperformance\senhancement,\sbut\sit\sis\sdifficult\sto\scome\sup\swith\sa\squery\swhere\nis\smakes\sa\ssignificant\sdifference.\s\sHence,\sthe\schange\sis\sgetting\sparked\nin\sa\sbranch.
+D 2014-02-26T19:05:53.265
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 2ef13430cd359f7b361bb863504e227b25cc7f81
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -172,7 +172,7 @@ F src/complete.c dc1d136c0feee03c2f7550bafc0d29075e36deac
 F src/ctime.c 77779efbe78dd678d84bfb4fc2e87b6b6ad8dccd
 F src/date.c 593c744b2623971e45affd0bde347631bdfa4625
 F src/delete.c cdd57149543bb28304d8f717c243f2a86b1fc280
-F src/expr.c 014b8087a15c4c314bdd798cb1cb0b32693f8b40
+F src/expr.c 0b84f62d653a74e1aa9f7fed39d65be74a32a125
 F src/fault.c 160a0c015b6c2629d3899ed2daf63d75754a32bb
 F src/fkey.c 5269ef07b100763134f71b889327c333bd0989cf
 F src/func.c f4499b39d66b71825514334ce67b32ff14bd19f5
@@ -216,12 +216,12 @@ F src/printf.c 85d07756e45d7496d19439dcae3e6e9e0090f269
 F src/random.c d10c1f85b6709ca97278428fd5db5bbb9c74eece
 F src/resolve.c ca8b99d894164435f5c55cb304c1b8121705c51e
 F src/rowset.c 64655f1a627c9c212d9ab497899e7424a34222e0
-F src/select.c 28bff39f9bc5ec618b0719fe3f7b4be9f88b6f02
+F src/select.c c959b4d9eb9b1e1adac37a5f792c9d6d3a7e561d
 F src/shell.c ca2b066ab31793532530e0c2fcf79e99628f3b2b
 F src/sqlite.h.in a2ef671f92747a5a1c8a47bad5c585a8dd9eca80
 F src/sqlite3.rc 11094cc6a157a028b301a9f06b3d03089ea37c3e
 F src/sqlite3ext.h 886f5a34de171002ad46fae8c36a7d8051c190fc
-F src/sqliteInt.h 46dfbe0b58282421188a6c25b6c0c0fae18e0134
+F src/sqliteInt.h 036e187f2b667a8315b949ebe0ed904ba1ba07a9
 F src/sqliteLimit.h 164b0e6749d31e0daa1a4589a169d31c0dec7b3d
 F src/status.c 7ac05a5c7017d0b9f0b4bcd701228b784f987158
 F src/table.c 2cd62736f845d82200acfa1287e33feb3c15d62e
@@ -290,7 +290,7 @@ F src/vtab.c 21b932841e51ebd7d075e2d0ad1415dce8d2d5fd
 F src/wal.c 76e7fc6de229bea8b30bb2539110f03a494dc3a8
 F src/wal.h df01efe09c5cb8c8e391ff1715cca294f89668a4
 F src/walker.c 11edb74d587bc87b33ca96a5173e3ec1b8389e45
-F src/where.c 6042e1a377cf7dc72c10493269ed75e276275cd8
+F src/where.c 655b8fc1858f58268945886648f98ca855c78dad
 F src/whereInt.h 921f935af8b684ffb49705610bda7284db1db138
 F test/8_3_names.test ebbb5cd36741350040fd28b432ceadf495be25b2
 F test/aggerror.test a867e273ef9e3d7919f03ef4f0e8c0d2767944f2
@@ -1152,7 +1152,10 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh d1a6de74685f360ab718efda6265994b99bbea01
 F tool/win/sqlite.vsix 030f3eeaf2cb811a3692ab9c14d021a75ce41fff
-P dca1945aeb3fb005263f9be00ee8e72b966ae303
-R 4bbcd8ca02f23a972c97ceb5ec0d3c0c
+P 9c2e7612cd137895e13ee872e668ce1216719d85
+R e4da2fed75cedad3cb42445a5f266f50
+T *branch * open-only-once
+T *sym-open-only-once *
+T -sym-trunk *
 U drh
-Z 998297c355a76316139497aa81dafb02
+Z e719204d25b226ef45e13c0c8ac591b5

manifest.uuid

@@ -1 +1 @@
-9c2e7612cd137895e13ee872e668ce1216719d85
+3ad687b7aa908b0e914be48cc8a21af5d07e52d9

src/expr.c

@@ -1868,6 +1868,7 @@ int sqlite3CodeSubselect(
       pSel->pLimit = sqlite3PExpr(pParse, TK_INTEGER, 0, 0,
                                   &sqlite3IntTokens[1]);
       pSel->iLimit = 0;
+      dest.wctrlFlags |= WHERE_OPEN_ONCE;
       if( sqlite3Select(pParse, pSel, &dest) ){
         return 0;
       }

src/select.c

@@ -37,6 +37,7 @@ static void clearSelect(sqlite3 *db, Select *p){
 */
 void sqlite3SelectDestInit(SelectDest *pDest, int eDest, int iParm){
   pDest->eDest = (u8)eDest;
+  pDest->wctrlFlags = 0;
   pDest->iSDParm = iParm;
   pDest->affSdst = 0;
   pDest->iSdst = 0;
@@ -1927,6 +1928,7 @@ static void generateWithRecursiveQuery(
   ** the value for the recursive-table. Store the results in the Queue.
   */
   p->pPrior = 0;
+  destQueue.wctrlFlags |= WHERE_OPEN_ONCE;
   sqlite3Select(pParse, p, &destQueue);
   assert( p->pPrior==0 );
   p->pPrior = pSetup;
@@ -4727,7 +4729,8 @@ int sqlite3Select(
 
   if( !isAgg && pGroupBy==0 ){
     /* No aggregate functions and no GROUP BY clause */
-    u16 wctrlFlags = (sDistinct.isTnct ? WHERE_WANT_DISTINCT : 0);
+    u16 wctrlFlags = (sDistinct.isTnct ? WHERE_WANT_DISTINCT : 0) 
+                     | pDest->wctrlFlags;
 
     /* Begin the database scan. */
     pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, pOrderBy, p->pEList,

src/sqliteInt.h

@@ -2075,6 +2075,7 @@ struct SrcList {
 #define WHERE_GROUPBY          0x0100 /* pOrderBy is really a GROUP BY */
 #define WHERE_DISTINCTBY       0x0200 /* pOrderby is really a DISTINCT clause */
 #define WHERE_WANT_DISTINCT    0x0400 /* All output needs to be distinct */
+#define WHERE_OPEN_ONCE        0x0800 /* Open on first iteration only */
 
 /* Allowed return values from sqlite3WhereIsDistinct()
 */
@@ -2269,6 +2270,7 @@ struct Select {
 struct SelectDest {
   u8 eDest;            /* How to dispose of the results.  On of SRT_* above. */
   char affSdst;        /* Affinity used when eDest==SRT_Set */
+  u16 wctrlFlags;      /* Extra flags for sqlite3WhereBegin() */
   int iSDParm;         /* A parameter used by the eDest disposal method */
   int iSdst;           /* Base register where results are written */
   int nSdst;           /* Number of registers allocated */

src/where.c

@@ -5673,6 +5673,7 @@ WhereInfo *sqlite3WhereBegin(
     Table *pTab;     /* Table to open */
     int iDb;         /* Index of database containing table/index */
     struct SrcList_item *pTabItem;
+    int addrOnce = 0;
 
     pTabItem = &pTabList->a[pLevel->iFrom];
     pTab = pTabItem->pTab;
@@ -5697,6 +5698,10 @@ WhereInfo *sqlite3WhereBegin(
         op = OP_OpenWrite;
         pWInfo->aiCurOnePass[0] = pTabItem->iCursor;
       };
+      if( wctrlFlags & WHERE_OPEN_ONCE ){
+        addrOnce = sqlite3CodeOnce(pParse);
+        VdbeCoverage(v);
+      }
       sqlite3OpenTable(pParse, pTabItem->iCursor, iDb, pTab, op);
       assert( pTabItem->iCursor==pLevel->iTabCur );
       testcase( !pWInfo->okOnePass && pTab->nCol==BMS-1 );
@@ -5740,6 +5745,7 @@ WhereInfo *sqlite3WhereBegin(
       sqlite3VdbeSetP4KeyInfo(pParse, pIx);
       VdbeComment((v, "%s", pIx->zName));
     }
+    if( addrOnce ) sqlite3VdbeJumpHere(v, addrOnce);
     if( iDb>=0 ) sqlite3CodeVerifySchema(pParse, iDb);
     notReady &= ~getMask(&pWInfo->sMaskSet, pTabItem->iCursor);
   }
@@ -5897,7 +5903,7 @@ void sqlite3WhereEnd(WhereInfo *pWInfo){
     */
     if( (pTab->tabFlags & TF_Ephemeral)==0
      && pTab->pSelect==0
-     && (pWInfo->wctrlFlags & WHERE_OMIT_OPEN_CLOSE)==0
+     && (pWInfo->wctrlFlags & (WHERE_OMIT_OPEN_CLOSE|WHERE_OPEN_ONCE))==0
     ){
       int ws = pLoop->wsFlags;
       if( !pWInfo->okOnePass && (ws & WHERE_IDX_ONLY)==0 ){