Add the count-of-view optimization when compiled using

SQLITE_COUNTOFVIEW_OPTIMIZATION.

FossilOrigin-Name: d1ba200234f40b84327c7fc28c2584ed069da80e97578df71114d1a9ba9c559c

manifest

@@ -1,5 +1,5 @@
-C Fix\sfurther\sOOM\shandling\scases\sin\sLSM.
-D 2017-07-04T19:23:32.815
+C Add\sthe\scount-of-view\soptimization\swhen\scompiled\susing\s\nSQLITE_COUNTOFVIEW_OPTIMIZATION.
+D 2017-07-04T19:34:36.404
 F Makefile.in 081e48dfe7f995d57ce1a88ddf4d2917b4349158648a6cd45b42beae30de3a12
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc 4ebb1d257cac7fb1bcb4ba59278416d410ff1c4bf59447a9c37a415f3516056a
@@ -448,12 +448,12 @@ F src/printf.c 8757834f1b54dae512fb25eb1acc8e94a0d15dd2290b58f2563f65973265adb2
 F src/random.c 80f5d666f23feb3e6665a6ce04c7197212a88384
 F src/resolve.c d1e69759e7a79c156c692793f5d16f82f9a60ce5e82efd95e4374b2423034946
 F src/rowset.c 7b7e7e479212e65b723bf40128c7b36dc5afdfac
-F src/select.c 741937503c74d85e64828b63d5a4219d3cfce480a717efef635839606001b1ba
+F src/select.c c9f7b7196e196e93979665680d055a789938b8e025556097bf484b184c0dd576
 F src/shell.c a2b148e4ca8eb81b96e1050207c83d4a16ea6bf9182374faee4dd2a43628c291
 F src/sqlite.h.in 651cba56f8df64ff4418aa981cdfd5bc2d65e5fef95c1671f9826f1a164a5fa3
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
 F src/sqlite3ext.h 58fd0676d3111d02e62e5a35992a7d3da5d3f88753acc174f2d37b774fbbdd28
-F src/sqliteInt.h 37f1a9a3266aa7b11126585314cd98cf11ba6f174b1244de2221270107ea754d
+F src/sqliteInt.h 35b98ec45550f4c32b09940aa5e7472927bf24a1eab7b8e6181c2b194ab0f950
 F src/sqliteLimit.h 1513bfb7b20378aa0041e7022d04acb73525de35b80b252f1b83fedb4de6a76b
 F src/status.c a9e66593dfb28a9e746cba7153f84d49c1ddc4b1
 F src/table.c b46ad567748f24a326d9de40e5b9659f96ffff34
@@ -529,7 +529,7 @@ F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
 F src/wal.c 40c543f0a2195d1b0dc88ef12142bea690009344
 F src/wal.h 06b2a0b599cc0f53ea97f497cf8c6b758c999f71
 F src/walker.c d46044e7a5842560dfe7122d93ff5145dd4a96f4d0bf5ba5910a7731b8c01e79
-F src/where.c 715b84912bf85d833ff558d6de51c0d0427483c1f5efe1bb6818d4e683f4869e
+F src/where.c e7cc80943459ade4ccaeb5c7c10f8a0db8b797e0b0f2509de7efc557b76bf7b6
 F src/whereInt.h 2a4b634d63ce488b46d4b0da8f2eaa8f9aeab202bc25ef76f007de5e3fba1f20
 F src/wherecode.c f17f5d51e372168db51af637e265aa5e80f99fcc81bfead96b66e71a7732bc62
 F src/whereexpr.c fa51927cc6830b9d3155cafa4e589452ec023fe313a56550d2079dca6c52fbd8
@@ -1628,7 +1628,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 989a5c1745a7145c14c6d9b713176ecba6b99296de8bdd09f666eeef10da9c2e
-R 922d647253bd2cf17b869e10d18fa4de
-U dan
-Z 09d57a8486afc6b09ffba0c342517c3e
+P ca757c8665e27de884086b2aab2bd1db481e2d12f2afe136ec151bf5a0e65b91
+R 2ca591b3293b9c66e5b306432bda9b33
+U drh
+Z 053a65d3705e0f808b1537da8a1f9e80

manifest.uuid

@@ -1 +1 @@
-ca757c8665e27de884086b2aab2bd1db481e2d12f2afe136ec151bf5a0e65b91
+d1ba200234f40b84327c7fc28c2584ed069da80e97578df71114d1a9ba9c559c

src/select.c

@@ -5017,6 +5017,88 @@ static struct SrcList_item *isSelfJoinView(
   return 0;
 }
 
+#ifdef SQLITE_COUNTOFVIEW_OPTIMIZATION
+/*
+** Attempt to transform a query of the form
+**
+**    SELECT count(*) FROM (SELECT x FROM t1 UNION ALL SELECT y FROM t2)
+**
+** Into this:
+**
+**    SELECT (SELECT count(*) FROM t1)+(SELECT count(*) FROM t2)
+**
+** The transformation only works if all of the following are true:
+**
+**   *  The subquery is a UNION ALL of two or more terms
+**   *  There is no WHERE or GROUP BY or HAVING clauses on the subqueries
+**   *  The outer query is a simple count(*)
+**
+** Return TRUE if the optimization is undertaken.
+*/
+static int countOfViewOptimization(Parse *pParse, Select *p){
+  Select *pSub, *pPrior;
+  Expr *pExpr;
+  Expr *pCount;
+  sqlite3 *db;
+  if( (p->selFlags & SF_Aggregate)==0 ) return 0;   /* This is an aggregate query */
+  if( p->pEList->nExpr!=1 ) return 0;               /* Single result column */
+  pExpr = p->pEList->a[0].pExpr;
+  if( pExpr->op!=TK_AGG_FUNCTION ) return 0;        /* Result is an aggregate */
+  if( sqlite3_stricmp(pExpr->u.zToken,"count") ) return 0;  /* Must be count() */
+  if( pExpr->x.pList!=0 ) return 0;                 /* Must be count(*) */
+  if( p->pSrc->nSrc!=1 ) return 0;                  /* One table in the FROM clause */
+  pSub = p->pSrc->a[0].pSelect;
+  if( pSub==0 ) return 0;                           /* The FROM is a subquery */
+  if( pSub->pPrior==0 ) return 0;                   /* Must be a compound subquery */
+  do{
+    if( pSub->op!=TK_ALL && pSub->pPrior ) return 0;  /* Must be UNION ALL */
+    if( pSub->pWhere ) return 0;                      /* No WHERE clause */
+    if( pSub->selFlags & SF_Aggregate ) return 0;     /* Not an aggregate */
+    pSub = pSub->pPrior;                              /* Repeat over compound terms */
+  }while( pSub );
+
+  /* If we reach this point, that means it is OK to perform the transformation */
+
+  db = pParse->db;
+  pCount = pExpr;
+  pExpr = 0;
+  pSub = p->pSrc->a[0].pSelect;
+  p->pSrc->a[0].pSelect = 0;
+  sqlite3SrcListDelete(db, p->pSrc);
+  p->pSrc = sqlite3DbMallocZero(pParse->db, sizeof(*p->pSrc));
+  while( pSub ){
+    Expr *pTerm;
+    pPrior = pSub->pPrior;
+    pSub->pPrior = 0;
+    pSub->pNext = 0;
+    pSub->selFlags |= SF_Aggregate;
+    pSub->selFlags &= ~SF_Compound;
+    pSub->nSelectRow = 0;
+    sqlite3ExprListDelete(db, pSub->pEList);
+    pTerm = pPrior ? sqlite3ExprDup(db, pCount, 0) : pCount;
+    pSub->pEList = sqlite3ExprListAppend(pParse, 0, pTerm);
+    pTerm = sqlite3PExpr(pParse, TK_SELECT, 0, 0);
+    sqlite3PExprAddSelect(pParse, pTerm, pSub);
+    if( pExpr==0 ){
+      pExpr = pTerm;
+    }else{
+      pExpr = sqlite3PExpr(pParse, TK_PLUS, pTerm, pExpr);
+    }
+    pSub = pPrior;
+  }
+  p->pEList->a[0].pExpr = pExpr;
+  p->selFlags &= ~SF_Aggregate;
+
+#if SELECTTRACE_ENABLED
+  if( sqlite3SelectTrace & 0x400 ){
+    SELECTTRACE(0x400,pParse,p,("After count-of-view optimization:\n"));
+    sqlite3TreeViewSelect(0, p, 0);
+  }
+#endif
+  return 1;
+}
+#endif /* SQLITE_COUNTOFVIEW_OPTIMIZATION */
+
 /*
 ** Generate code for the SELECT statement given in the p argument.  
 **
@@ -5329,6 +5411,16 @@ int sqlite3Select(
   }
 #endif
 
+#ifdef SQLITE_COUNTOFVIEW_OPTIMIZATION
+  if( OptimizationEnabled(db, SQLITE_QueryFlattener|SQLITE_CountOfView)
+   && countOfViewOptimization(pParse, p)
+  ){
+    if( db->mallocFailed ) goto select_end;
+    pEList = p->pEList;
+    pTabList = p->pSrc;
+  }
+#endif
+
   /* If the query is DISTINCT with an ORDER BY but is not an aggregate, and 
   ** if the select-list is the same as the ORDER BY list, then this query
   ** can be rewritten as a GROUP BY. In other words, this:

src/sqliteInt.h

@@ -1509,6 +1509,7 @@ struct sqlite3 {
 #define SQLITE_Transitive     0x0200   /* Transitive constraints */
 #define SQLITE_OmitNoopJoin   0x0400   /* Omit unused tables in joins */
 #define SQLITE_Stat34         0x0800   /* Use STAT3 or STAT4 data */
+#define SQLITE_CountOfView    0x1000   /* The count-of-view optimization */
 #define SQLITE_CursorHints    0x2000   /* Add OP_CursorHint opcodes */
 #define SQLITE_AllOpts        0xffff   /* All optimizations */
 

src/where.c

@@ -4549,9 +4549,13 @@ WhereInfo *sqlite3WhereBegin(
     sqlite3WhereTabFuncArgs(pParse, &pTabList->a[ii], &pWInfo->sWC);
   }
 #ifdef SQLITE_DEBUG
-  for(ii=0; ii<pTabList->nSrc; ii++){
-    Bitmask m = sqlite3WhereGetMask(pMaskSet, pTabList->a[ii].iCursor);
-    assert( m==MASKBIT(ii) );
+  {
+    Bitmask mx = 0;
+    for(ii=0; ii<pTabList->nSrc; ii++){
+      Bitmask m = sqlite3WhereGetMask(pMaskSet, pTabList->a[ii].iCursor);
+      assert( m>=mx );
+      mx = m;
+    }
   }
 #endif