Materialize any CTE that is used more than once.

Author: D. Richard Hipp

src/delete.c

@@ -209,7 +209,11 @@ Expr *sqlite3LimitWhere(
   pSrc->a[0].pTab = 0;
   pSelectSrc = sqlite3SrcListDup(pParse->db, pSrc, 0);
   pSrc->a[0].pTab = pTab;
-  pSrc->a[0].pIBIndex = 0;
+  if( pSrc->a[0].fg.isIndexedBy ){
+    pSrc->a[0].u2.pIBIndex = 0;
+  }else if( pSrc->a[0].fg.isCte ){
+    pSrc->a[0].u2.pCteUse->nUse++;
+  }
 
   /* generate the SELECT expression tree. */
   pSelect = sqlite3SelectNew(pParse, pEList, pSelectSrc, pWhere, 0 ,0, 

src/expr.c

@@ -1544,7 +1544,10 @@ SrcList *sqlite3SrcListDup(sqlite3 *db, SrcList *p, int flags){
     if( pNewItem->fg.isIndexedBy ){
       pNewItem->u1.zIndexedBy = sqlite3DbStrDup(db, pOldItem->u1.zIndexedBy);
     }
-    pNewItem->pIBIndex = pOldItem->pIBIndex;
+    pNewItem->u2 = pOldItem->u2;
+    if( pNewItem->fg.isCte ){
+      pNewItem->u2.pCteUse->nUse++;
+    }
     if( pNewItem->fg.isTabFunc ){
       pNewItem->u1.pFuncArg = 
           sqlite3ExprListDup(db, pOldItem->u1.pFuncArg, flags);

src/prepare.c

@@ -597,7 +597,7 @@ void sqlite3ParserReset(Parse *pParse){
 **
 **       testcase( pParse->earlyCleanup );
 */
-void sqlite3ParserAddCleanup(
+void *sqlite3ParserAddCleanup(
   Parse *pParse,                      /* Destroy when this Parser finishes */
   void (*xCleanup)(sqlite3*,void*),   /* The cleanup routine */
   void *pPtr                          /* Pointer to object to be cleaned up */
@@ -610,10 +610,12 @@ void sqlite3ParserAddCleanup(
     pCleanup->xCleanup = xCleanup;
   }else{
     xCleanup(pParse->db, pPtr);
+    pPtr = 0;
 #if defined(SQLITE_DEBUG) || defined(SQLITE_COVERAGE_TEST)
     pParse->earlyCleanup = 1;
 #endif
   }
+  return pPtr;
 }
 
 /*

src/select.c

@@ -4726,7 +4726,7 @@ int sqlite3IndexedByLookup(Parse *pParse, SrcItem *pFrom){
     pParse->checkSchema = 1;
     return SQLITE_ERROR;
   }
-  pFrom->pIBIndex = pIdx;
+  pFrom->u2.pIBIndex = pIdx;
   return SQLITE_OK;
 }
 
@@ -4935,8 +4935,18 @@ static int resolveFromTermToCte(
     if( cannotBeFunction(pParse, pFrom) ) return 2;
 
     assert( pFrom->pTab==0 );
-    pFrom->pTab = pTab = sqlite3DbMallocZero(db, sizeof(Table));
+    pTab = sqlite3DbMallocZero(db, sizeof(Table));
     if( pTab==0 ) return 2;
+    if( pCte->pUse==0 ){
+      pCte->pUse = sqlite3DbMallocZero(db, sizeof(pCte->pUse[0]));
+      if( pCte->pUse==0
+       || sqlite3ParserAddCleanup(pParse,sqlite3DbFree,pCte->pUse)==0
+      ){
+        sqlite3DbFree(db, pTab);
+        return 2;
+      }
+    }
+    pFrom->pTab = pTab;
     pTab->nTabRef = 1;
     pTab->zName = sqlite3DbStrDup(db, pCte->zName);
     pTab->iPKey = -1;
@@ -4945,6 +4955,9 @@ static int resolveFromTermToCte(
     pFrom->pSelect = sqlite3SelectDup(db, pCte->pSelect, 0);
     if( db->mallocFailed ) return 2;
     assert( pFrom->pSelect );
+    pFrom->fg.isCte = 1;
+    pFrom->u2.pCteUse = pCte->pUse;
+    pCte->pUse->nUse++;
 
     /* Check if this is a recursive CTE. */
     pRecTerm = pSel = pFrom->pSelect;
@@ -6153,6 +6166,7 @@ int sqlite3Select(
   */
   for(i=0; i<pTabList->nSrc; i++){
     SrcItem *pItem = &pTabList->a[i];
+    SrcItem *pPrior;
     SelectDest dest;
     Select *pSub;
 #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
@@ -6212,6 +6226,7 @@ int sqlite3Select(
     ** inside the subquery.  This can help the subquery to run more efficiently.
     */
     if( OptimizationEnabled(db, SQLITE_PushDown)
+     && (pItem->fg.isCte==0 || pItem->u2.pCteUse->nUse<=1)
      && pushDownWhereTerms(pParse, pSub, p->pWhere, pItem->iCursor,
                            (pItem->fg.jointype & JT_OUTER)!=0)
     ){
@@ -6232,16 +6247,18 @@ int sqlite3Select(
 
     /* Generate code to implement the subquery
     **
-    ** The subquery is implemented as a co-routine if the subquery is
-    ** guaranteed to be the outer loop (so that it does not need to be
-    ** computed more than once)
+    ** The subquery is implemented as a co-routine if:
+    **    (1)  the subquery is guaranteed to be the outer loop (so that
+    **         it does not need to be computed more than once), and
+    **    (2)  the subquery is not a CTE that is used more then once.
     **
-    ** TODO: Are there other reasons beside (1) to use a co-routine
+    ** TODO: Are there other reasons beside (1) and (2) to use a co-routine
     ** implementation?
     */
     if( i==0
      && (pTabList->nSrc==1
             || (pTabList->a[1].fg.jointype&(JT_LEFT|JT_CROSS))!=0)  /* (1) */
+     && (pItem->fg.isCte==0 || pItem->u2.pCteUse->nUse<2)           /* (2) */
     ){
       /* Implement a co-routine that will return a single row of the result
       ** set on each invocation.
@@ -6261,16 +6278,30 @@ int sqlite3Select(
       sqlite3VdbeEndCoroutine(v, pItem->regReturn);
       sqlite3VdbeJumpHere(v, addrTop-1);
       sqlite3ClearTempRegCache(pParse);
+    }else if( pItem->fg.isCte && pItem->u2.pCteUse->addrM9e>0 ){
+      /* This is a CTE for which materialization code has already been
+      ** generated.  Invoke the subroutine to compute the materialization,
+      ** the make the pItem->iCursor be a copy of the ephemerial table that
+      ** holds the result of the materialization. */
+      CteUse *pCteUse = pItem->u2.pCteUse;
+      sqlite3VdbeAddOp2(v, OP_Gosub, pCteUse->regRtn, pCteUse->addrM9e);
+      if( pItem->iCursor!=pCteUse->iCur ){
+        sqlite3VdbeAddOp2(v, OP_OpenDup, pItem->iCursor, pCteUse->iCur);
+      }
+      pSub->nSelectRow = pCteUse->nRowEst;
+    }else if( (pPrior = isSelfJoinView(pTabList, pItem))!=0 ){
+      /* This view has already been materialized by a prior entry in
+      ** this same FROM clause.  Reuse it. */
+      if( pPrior->addrFillSub ){
+        sqlite3VdbeAddOp2(v, OP_Gosub, pPrior->regReturn, pPrior->addrFillSub);
+      }
+      sqlite3VdbeAddOp2(v, OP_OpenDup, pItem->iCursor, pPrior->iCursor);
+      pSub->nSelectRow = pPrior->pSelect->nSelectRow;
     }else{
-      /* Generate a subroutine that will fill an ephemeral table with
-      ** the content of this subquery.  pItem->addrFillSub will point
-      ** to the address of the generated subroutine.  pItem->regReturn
-      ** is a register allocated to hold the subroutine return address
-      */
+      /* Generate a subroutine that will materialize the view. */
       int topAddr;
       int onceAddr = 0;
       int retAddr;
-      SrcItem *pPrior;
 
       testcase( pItem->addrFillSub==0 ); /* Ticket c52b09c7f38903b1311 */
       pItem->regReturn = ++pParse->nMem;
@@ -6285,22 +6316,22 @@ int sqlite3Select(
       }else{
         VdbeNoopComment((v, "materialize \"%s\"", pItem->pTab->zName));
       }
-      pPrior = isSelfJoinView(pTabList, pItem);
-      if( pPrior ){
-        sqlite3VdbeAddOp2(v, OP_OpenDup, pItem->iCursor, pPrior->iCursor);
-        assert( pPrior->pSelect!=0 );
-        pSub->nSelectRow = pPrior->pSelect->nSelectRow;
-      }else{
-        sqlite3SelectDestInit(&dest, SRT_EphemTab, pItem->iCursor);
-        ExplainQueryPlan((pParse, 1, "MATERIALIZE %u", pSub->selId));
-        sqlite3Select(pParse, pSub, &dest);
-      }
+      sqlite3SelectDestInit(&dest, SRT_EphemTab, pItem->iCursor);
+      ExplainQueryPlan((pParse, 1, "MATERIALIZE %u", pSub->selId));
+      sqlite3Select(pParse, pSub, &dest);
       pItem->pTab->nRowLogEst = pSub->nSelectRow;
       if( onceAddr ) sqlite3VdbeJumpHere(v, onceAddr);
       retAddr = sqlite3VdbeAddOp1(v, OP_Return, pItem->regReturn);
       VdbeComment((v, "end %s", pItem->pTab->zName));
       sqlite3VdbeChangeP1(v, topAddr, retAddr);
       sqlite3ClearTempRegCache(pParse);
+      if( pItem->fg.isCte ){
+        CteUse *pCteUse = pItem->u2.pCteUse;
+        pCteUse->addrM9e = pItem->addrFillSub;
+        pCteUse->regRtn = pItem->regReturn;
+        pCteUse->iCur = pItem->iCursor;
+        pCteUse->nRowEst = pSub->nSelectRow;
+      }
     }
     if( db->mallocFailed ) goto select_end;
     pParse->nHeight -= sqlite3SelectExprHeight(p);

src/sqliteInt.h

@@ -1137,6 +1137,7 @@ typedef struct Bitvec Bitvec;
 typedef struct CollSeq CollSeq;
 typedef struct Column Column;
 typedef struct Cte Cte;
+typedef struct CteUse CteUse;
 typedef struct Db Db;
 typedef struct DbFixer DbFixer;
 typedef struct Schema Schema;
@@ -2941,6 +2942,7 @@ struct SrcItem {
     unsigned viaCoroutine :1;  /* Implemented as a co-routine */
     unsigned isRecursive :1;   /* True for recursive reference in WITH */
     unsigned fromDDL :1;       /* Comes from sqlite_schema */
+    unsigned isCte :1;         /* This is a CTE */
   } fg;
   int iCursor;      /* The VDBE cursor number used to access this table */
   Expr *pOn;        /* The ON clause of a join */
@@ -2950,7 +2952,10 @@ struct SrcItem {
     char *zIndexedBy;    /* Identifier from "INDEXED BY <zIndex>" clause */
     ExprList *pFuncArg;  /* Arguments to table-valued-function */
   } u1;
-  Index *pIBIndex;  /* Index structure corresponding to u1.zIndexedBy */
+  union {
+    Index *pIBIndex;  /* Index structure corresponding to u1.zIndexedBy */
+    CteUse *pCteUse;  /* CTE Usage info info fg.isCte is true */
+  } u2;
 };
 
 /*
@@ -3889,6 +3894,7 @@ struct Cte {
   ExprList *pCols;        /* List of explicit column names, or NULL */
   Select *pSelect;        /* The definition of this CTE */
   const char *zCteErr;    /* Error message for circular references */
+  CteUse *pUse;           /* Usage information for this CTE */
 };
 
 /*
@@ -3901,6 +3907,26 @@ struct With {
   Cte a[1];               /* For each CTE in the WITH clause.... */
 };
 
+/*
+** The Cte object is not guaranteed to persist for the entire duration
+** of code generation.  (The query flattener or other parser tree
+** edits might delete it.)  The following object records information
+** about each Common Table Expression that must be preserved for the
+** duration of the parse.
+**
+** The CteUse objects are freed using sqlite3ParserAddCleanup() rather
+** than sqlite3SelectDelete(), which is what enables them to persist
+** until the end of code generation.
+*/
+struct CteUse {
+  int nUse;              /* Number of users of this CTE */
+  int addrM9e;           /* Start of subroutine to compute materialization */
+  int regRtn;            /* Return address register for addrM9e subroutine */
+  int iCur;              /* Ephemeral table holding the materialization */
+  LogEst nRowEst;        /* Estimated number of rows in the table */
+};
+
+
 #ifdef SQLITE_DEBUG
 /*
 ** An instance of the TreeView object is used for printing the content of
@@ -4889,7 +4915,7 @@ sqlite3_int64 sqlite3StmtCurrentTime(sqlite3_context*);
 int sqlite3VdbeParameterIndex(Vdbe*, const char*, int);
 int sqlite3TransferBindings(sqlite3_stmt *, sqlite3_stmt *);
 void sqlite3ParserReset(Parse*);
-void sqlite3ParserAddCleanup(Parse*,void(*)(sqlite3*,void*),void*);
+void *sqlite3ParserAddCleanup(Parse*,void(*)(sqlite3*,void*),void*);
 #ifdef SQLITE_ENABLE_NORMALIZE
 char *sqlite3Normalize(Vdbe*, const char*);
 #endif

src/treeview.c

@@ -111,7 +111,10 @@ void sqlite3TreeViewWith(TreeView *pView, const With *pWith, u8 moreToFollow){
         }
         sqlite3_str_appendf(&x, ")");
       }
-      sqlite3_str_appendf(&x, " AS");
+      if( pCte->pUse ){
+        sqlite3_str_appendf(&x, " (pUse=0x%p, nUse=%d)", pCte->pUse,
+                 pCte->pUse->nUse);
+      }
       sqlite3StrAccumFinish(&x);
       sqlite3TreeViewItem(pView, zLine, i<pWith->nCte-1);
       sqlite3TreeViewSelect(pView, pCte->pSelect, 0);
@@ -150,6 +153,9 @@ void sqlite3TreeViewSrcList(TreeView *pView, const SrcList *pSrc){
     if( pItem->fg.fromDDL ){
       sqlite3_str_appendf(&x, " DDL");
     }
+    if( pItem->fg.isCte ){
+      sqlite3_str_appendf(&x, " CteUse=0x%p", pItem->u2.pCteUse);
+    }
     sqlite3StrAccumFinish(&x);
     sqlite3TreeViewItem(pView, zLine, i<pSrc->nSrc-1); 
     if( pItem->pSelect ){

src/where.c

@@ -2956,7 +2956,7 @@ static int whereLoopAddBtree(
 
   if( pSrc->fg.isIndexedBy ){
     /* An INDEXED BY clause specifies a particular index to use */
-    pProbe = pSrc->pIBIndex;
+    pProbe = pSrc->u2.pIBIndex;
   }else if( !HasRowid(pTab) ){
     pProbe = pTab->pIndex;
   }else{