Clarification and simplification and result column naming logic.

FossilOrigin-Name: 68824a439b76a4cca05609a02de7abdc42bd1d26afbfcd047b90001c610d3c56

manifest

@@ -1,5 +1,5 @@
-C Fix\sa\sproblem\sin\san\slsmtest\stest\scase\scaused\sby\swriting\sdata\sin\s"text"\smode\ninstead\sof\s"binary".
+C Clarification\sand\ssimplification\sand\sresult\scolumn\snaming\slogic.
-D 2017-07-12T14:03:13.542
+D 2017-07-12T14:10:19.869
 F Makefile.in 081e48dfe7f995d57ce1a88ddf4d2917b4349158648a6cd45b42beae30de3a12
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc 20850e3e8d4d4791e0531955852d768eb06f24138214870d543abb1a47346fba
@@ -449,7 +449,7 @@ F src/printf.c 8757834f1b54dae512fb25eb1acc8e94a0d15dd2290b58f2563f65973265adb2
 F src/random.c 80f5d666f23feb3e6665a6ce04c7197212a88384
 F src/resolve.c 6aa1fb1212e601f65b983ee1215d69a591986c8f97a3805c425c625a53839539
 F src/rowset.c 7b7e7e479212e65b723bf40128c7b36dc5afdfac
-F src/select.c 6aa7e8ee53dcb9d0b77b05670bb44a1076d6747bc9b2c1f12a365b553ab6c828
+F src/select.c 95659b7990e390f9bd8dc30b8975c675fcd1d46e569bc4f5a14e22a8d03e3d14
 F src/shell.c 0401a716fc5343594b8ee60ce065d9a71373d3403f0b81f9fed684741e6401d1
 F src/shell.c.in 98bfdeeb0808418b37f59e6d380568a76e0733efe2494377096f434b39940cad
 F src/sqlite.h.in 03a422ba13da1dfef7f1aaa1ba344acf18dc867112620b1fdb2a1426cabba634
@@ -1631,7 +1631,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
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+U drh
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+Z 4894df80f0f6930b7360c2bd22600907

manifest.uuid

@@ -1 +1 @@
-3e56a79ad8754e6da3181883154fa1c8b227a8d16c9b2a3eba925371595ae1f9
+68824a439b76a4cca05609a02de7abdc42bd1d26afbfcd047b90001c610d3c56

src/select.c

@@ -1568,20 +1568,46 @@ static Table *tableWithCursor(SrcList *pList, int iCursor){
 
 
 /*
-** Generate code that will tell the VDBE the names of columns
+** Compute the column names for a SELECT statement.
-** in the result set.  This information is used to provide the
+**
-** azCol[] values in the callback.
+** The only guarantee that SQLite makes about column names is that if the
+** column has an AS clause assigning it a name, that will be the name used.
+** That is the only documented guarantee.  However, countless applications
+** developed over the years have made baseless assumptions about column names
+** and will break if those assumptions changes.  Hence, use extreme caution
+** when modifying this routine to avoid breaking legacy.
+**
+** See Also: sqlite3ColumnsFromExprList()
+**
+** The PRAGMA short_column_names and PRAGMA full_column_names settings are
+** deprecated.  The default setting is short=ON, full=OFF.  99.9% of all
+** applications should operate this way.  Nevertheless, we need to support the
+** other modes for legacy:
+**
+**    short=OFF, full=OFF:      Column name is the text of the expression has it
+**                              originally appears in the SELECT statement.  In
+**                              other words, the zSpan of the result expression.
+**
+**    short=ON, full=OFF:       (This is the default setting).  If the result
+**                              refers directly to a table column, then the result
+**                              column name is just the table column name: COLUMN. 
+**                              Otherwise use zSpan.
+**
+**    full=ON, short=ANY:       If the result refers directly to a table column,
+**                              then the result column name with the table name
+**                              prefix, ex: TABLE.COLUMN.  Otherwise use zSpan.
 */
 static void generateColumnNames(
   Parse *pParse,      /* Parser context */
-  SrcList *pTabList,  /* List of tables */
+  SrcList *pTabList,  /* The FROM clause of the SELECT */
   ExprList *pEList    /* Expressions defining the result set */
 ){
   Vdbe *v = pParse->pVdbe;
   int i;
   Table *pTab;
   sqlite3 *db = pParse->db;
-  int fullNames, shortNames;
+  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 */
@@ -1594,17 +1620,19 @@ static void generateColumnNames(
   assert( v!=0 );
   assert( pTabList!=0 );
   pParse->colNamesSet = 1;
-  fullNames = (db->flags & SQLITE_FullColNames)!=0;
+  fullName = (db->flags & SQLITE_FullColNames)!=0;
-  shortNames = (db->flags & SQLITE_ShortColNames)!=0;
+  srcName = (db->flags & SQLITE_ShortColNames)!=0 || fullName;
   sqlite3VdbeSetNumCols(v, pEList->nExpr);
   for(i=0; i<pEList->nExpr; i++){
-    Expr *p;
+    Expr *p = pEList->a[i].pExpr;
-    p = pEList->a[i].pExpr;
+
-    if( NEVER(p==0) ) continue;
+    assert( p!=0 );
     if( pEList->a[i].zName ){
+      /* An AS clause always takes first priority */
       char *zName = pEList->a[i].zName;
       sqlite3VdbeSetColName(v, i, COLNAME_NAME, zName, SQLITE_TRANSIENT);
-    }else if( (p->op==TK_COLUMN || p->op==TK_AGG_COLUMN)
+    }else if( srcName
+           && (p->op==TK_COLUMN || p->op==TK_AGG_COLUMN)
            && (pTab = tableWithCursor(pTabList, p->iTable))!=0
     ){
       char *zCol;
@@ -1616,10 +1644,7 @@ static void generateColumnNames(
       }else{
         zCol = pTab->aCol[iCol].zName;
       }
-      if( !shortNames && !fullNames ){
+      if( fullName ){
-        sqlite3VdbeSetColName(v, i, COLNAME_NAME, 
-            sqlite3DbStrDup(db, pEList->a[i].zSpan), SQLITE_DYNAMIC);
-      }else if( fullNames ){
         char *zName = 0;
         zName = sqlite3MPrintf(db, "%s.%s", pTab->zName, zCol);
         sqlite3VdbeSetColName(v, i, COLNAME_NAME, zName, SQLITE_DYNAMIC);
@@ -1647,6 +1672,15 @@ static void generateColumnNames(
 **
 ** Return SQLITE_OK on success.  If a memory allocation error occurs,
 ** store NULL in *paCol and 0 in *pnCol and return SQLITE_NOMEM.
+**
+** The only guarantee that SQLite makes about column names is that if the
+** column has an AS clause assigning it a name, that will be the name used.
+** That is the only documented guarantee.  However, countless applications
+** developed over the years have made baseless assumptions about column names
+** and will break if those assumptions changes.  Hence, use extreme caution
+** when modifying this routine to avoid breaking legacy.
+**
+** See Also: generateColumnNames()
 */
 int sqlite3ColumnsFromExprList(
   Parse *pParse,          /* Parsing context */
@@ -1659,7 +1693,6 @@ int sqlite3ColumnsFromExprList(
   u32 cnt;                    /* Index added to make the name unique */
   Column *aCol, *pCol;        /* For looping over result columns */
   int nCol;                   /* Number of columns in the result set */
-  Expr *p;                    /* Expression for a single result column */
   char *zName;                /* Column name */
   int nName;                  /* Size of name in zName[] */
   Hash ht;                    /* Hash table of column names */
@@ -1680,12 +1713,10 @@ int sqlite3ColumnsFromExprList(
   for(i=0, pCol=aCol; i<nCol && !db->mallocFailed; i++, pCol++){
     /* Get an appropriate name for the column
     */
-    p = sqlite3ExprSkipCollate(pEList->a[i].pExpr);
     if( (zName = pEList->a[i].zName)!=0 ){
       /* If the column contains an "AS <name>" phrase, use <name> as the name */
     }else{
-      Expr *pColExpr = p;  /* The expression that is the result column name */
+      Expr *pColExpr = sqlite3ExprSkipCollate(pEList->a[i].pExpr);
-      Table *pTab;         /* Table associated with this expression */
       while( pColExpr->op==TK_DOT ){
         pColExpr = pColExpr->pRight;
         assert( pColExpr!=0 );
@@ -1693,7 +1724,7 @@ int sqlite3ColumnsFromExprList(
       if( pColExpr->op==TK_COLUMN && pColExpr->pTab!=0 ){
         /* For columns use the column name name */
         int iCol = pColExpr->iColumn;
-        pTab = pColExpr->pTab;
+        Table *pTab = pColExpr->pTab;
         if( iCol<0 ) iCol = pTab->iPKey;
         zName = iCol>=0 ? pTab->aCol[iCol].zName : "rowid";
       }else if( pColExpr->op==TK_ID ){