Move the generation of output column names earlier, to right after

name resolution and before query transformations such as flattening. 
This prevents the names from getting mangled by query transformations, 
and obviates hacks in the query flattener that attempt to work around 
the name mangling. The resulting code is smaller and faster and gives
more consistent output. Fix to ticket [de3403bf5ae5f72ed].

FossilOrigin-Name: ade7ddf1998190b2b630715774963150d86bed3211b7fd600cbf3068427e1531

1 files changed, 21 insertions, 62 deletions

diff --git a/src/select.c b/src/select.c
index a3ada4ef7..9af93dc9e 100644
--- a/src/select.c
+++ b/src/select.c
@@ -1438,13 +1438,10 @@ static const char *columnTypeImpl(
         ** of the SELECT statement. Return the declaration type and origin
         ** data for the result-set column of the sub-select.
         */
-        if( iCol>=0 && ALWAYS(iCol<pS->pEList->nExpr) ){
+        if( iCol>=0 && iCol<pS->pEList->nExpr ){
           /* If iCol is less than zero, then the expression requests the
           ** rowid of the sub-select or view. This expression is legal (see 
           ** test case misc2.2.2) - it always evaluates to NULL.
-          **
-          ** The ALWAYS() is because iCol>=pS->pEList->nExpr will have been
-          ** caught already by name resolution.
           */
           NameContext sNC;
           Expr *p = pS->pEList->a[iCol].pExpr;
@@ -1554,18 +1551,6 @@ static void generateColumnTypes(
 #endif /* !defined(SQLITE_OMIT_DECLTYPE) */
 }
 
-/*
-** Return the Table objecct in the SrcList that has cursor iCursor.
-** Or return NULL if no such Table object exists in the SrcList.
-*/
-static Table *tableWithCursor(SrcList *pList, int iCursor){
-  int j;
-  for(j=0; j<pList->nSrc; j++){
-    if( pList->a[j].iCursor==iCursor ) return pList->a[j].pTab;
-  }
-  return 0;
-}
-
 
 /*
 ** Compute the column names for a SELECT statement.
@@ -1599,15 +1584,16 @@ static Table *tableWithCursor(SrcList *pList, int iCursor){
 */
 static void generateColumnNames(
   Parse *pParse,      /* Parser context */
-  SrcList *pTabList,  /* The FROM clause of the SELECT */
-  ExprList *pEList    /* Expressions defining the result set */
+  Select *pSelect     /* Generate column names for this SELECT statement */
 ){
   Vdbe *v = pParse->pVdbe;
   int i;
   Table *pTab;
+  SrcList *pTabList;
+  ExprList *pEList;
   sqlite3 *db = pParse->db;
-  int fullName;      /* TABLE.COLUMN if no AS clause and is a direct table ref */
-  int srcName;       /* COLUMN or TABLE.COLUMN if no AS clause and is direct */
+  int fullName;    /* TABLE.COLUMN if no AS clause and is a direct table ref */
+  int srcName;     /* COLUMN or TABLE.COLUMN if no AS clause and is direct */
 
 #ifndef SQLITE_OMIT_EXPLAIN
   /* If this is an EXPLAIN, skip this step */
@@ -1617,6 +1603,10 @@ static void generateColumnNames(
 #endif
 
   if( pParse->colNamesSet || db->mallocFailed ) return;
+  /* Column names are determined by the left-most term of a compound select */
+  while( pSelect->pPrior ) pSelect = pSelect->pPrior;
+  pTabList = pSelect->pSrc;
+  pEList = pSelect->pEList;
   assert( v!=0 );
   assert( pTabList!=0 );
   pParse->colNamesSet = 1;
@@ -1631,12 +1621,11 @@ static void generateColumnNames(
       /* An AS clause always takes first priority */
       char *zName = pEList->a[i].zName;
       sqlite3VdbeSetColName(v, i, COLNAME_NAME, zName, SQLITE_TRANSIENT);
-    }else if( srcName
-           && (p->op==TK_COLUMN || p->op==TK_AGG_COLUMN)
-           && (pTab = tableWithCursor(pTabList, p->iTable))!=0
-    ){
+    }else if( srcName && p->op==TK_COLUMN ){
       char *zCol;
       int iCol = p->iColumn;
+      pTab = p->pTab;
+      assert( pTab!=0 );
       if( iCol<0 ) iCol = pTab->iPKey;
       assert( iCol==-1 || (iCol>=0 && iCol<pTab->nCol) );
       if( iCol<0 ){
@@ -2468,11 +2457,6 @@ static int multiSelect(
       if( dest.eDest!=priorOp ){
         int iCont, iBreak, iStart;
         assert( p->pEList );
-        if( dest.eDest==SRT_Output ){
-          Select *pFirst = p;
-          while( pFirst->pPrior ) pFirst = pFirst->pPrior;
-          generateColumnNames(pParse, pFirst->pSrc, pFirst->pEList);
-        }
         iBreak = sqlite3VdbeMakeLabel(v);
         iCont = sqlite3VdbeMakeLabel(v);
         computeLimitRegisters(pParse, p, iBreak);
@@ -2543,11 +2527,6 @@ static int multiSelect(
       ** tables.
       */
       assert( p->pEList );
-      if( dest.eDest==SRT_Output ){
-        Select *pFirst = p;
-        while( pFirst->pPrior ) pFirst = pFirst->pPrior;
-        generateColumnNames(pParse, pFirst->pSrc, pFirst->pEList);
-      }
       iBreak = sqlite3VdbeMakeLabel(v);
       iCont = sqlite3VdbeMakeLabel(v);
       computeLimitRegisters(pParse, p, iBreak);
@@ -3155,14 +3134,6 @@ static int multiSelectOrderBy(
   */
   sqlite3VdbeResolveLabel(v, labelEnd);
 
-  /* Set the number of output columns
-  */
-  if( pDest->eDest==SRT_Output ){
-    Select *pFirst = pPrior;
-    while( pFirst->pPrior ) pFirst = pFirst->pPrior;
-    generateColumnNames(pParse, pFirst->pSrc, pFirst->pEList);
-  }
-
   /* Reassembly the compound query so that it will be freed correctly
   ** by the calling function */
   if( p->pPrior ){
@@ -3457,7 +3428,6 @@ static int flattenSubquery(
   Select *pSub1;      /* Pointer to the rightmost select in sub-query */
   SrcList *pSrc;      /* The FROM clause of the outer query */
   SrcList *pSubSrc;   /* The FROM clause of the subquery */
-  ExprList *pList;    /* The result set of the outer query */
   int iParent;        /* VDBE cursor number of the pSub result set temp table */
   int iNewParent = -1;/* Replacement table for iParent */
   int isLeftJoin = 0; /* True if pSub is the right side of a LEFT JOIN */    
@@ -3782,14 +3752,6 @@ static int flattenSubquery(
     ** We look at every expression in the outer query and every place we see
     ** "a" we substitute "x*3" and every place we see "b" we substitute "y+10".
     */
-    pList = pParent->pEList;
-    for(i=0; i<pList->nExpr; i++){
-      if( pList->a[i].zName==0 ){
-        char *zName = sqlite3DbStrDup(db, pList->a[i].zSpan);
-        sqlite3Dequote(zName);
-        pList->a[i].zName = zName;
-      }
-    }
     if( pSub->pOrderBy ){
       /* At this point, any non-zero iOrderByCol values indicate that the
       ** ORDER BY column expression is identical to the iOrderByCol'th
@@ -5219,6 +5181,14 @@ int sqlite3Select(
   }
 #endif
 
+  /* Get a pointer the VDBE under construction, allocating a new VDBE if one
+  ** does not already exist */
+  v = sqlite3GetVdbe(pParse);
+  if( v==0 ) goto select_end;
+  if( pDest->eDest==SRT_Output ){
+    generateColumnNames(pParse, p);
+  }
+
   /* Try to flatten subqueries in the FROM clause up into the main query
   */
 #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
@@ -5254,11 +5224,6 @@ int sqlite3Select(
   }
 #endif
 
-  /* Get a pointer the VDBE under construction, allocating a new VDBE if one
-  ** does not already exist */
-  v = sqlite3GetVdbe(pParse);
-  if( v==0 ) goto select_end;
-
 #ifndef SQLITE_OMIT_COMPOUND_SELECT
   /* Handle compound SELECT statements using the separate multiSelect()
   ** procedure.
@@ -6058,12 +6023,6 @@ int sqlite3Select(
 select_end:
   explainSetInteger(pParse->iSelectId, iRestoreSelectId);
 
-  /* Identify column names if results of the SELECT are to be output.
-  */
-  if( rc==SQLITE_OK && pDest->eDest==SRT_Output ){
-    generateColumnNames(pParse, pTabList, pEList);
-  }
-
   sqlite3DbFree(db, sAggInfo.aCol);
   sqlite3DbFree(db, sAggInfo.aFunc);
 #if SELECTTRACE_ENABLED