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Overview
Comment:Clarification and simplification and result column naming logic.
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SHA3-256: 68824a439b76a4cca05609a02de7abdc42bd1d26afbfcd047b90001c610d3c56
User & Date: drh 2017-07-12 14:10:19
Context
2017-07-12
17:08
The EP_Resolved flag on the Expr object is not required for correctness nor performance, so remove it. check-in: 54f55d3b user: drh tags: trunk
14:10
Clarification and simplification and result column naming logic. check-in: 68824a43 user: drh tags: trunk
14:03
Fix a problem in an lsmtest test case caused by writing data in "text" mode instead of "binary". check-in: 3e56a79a user: dan tags: trunk
Changes
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Changes to src/select.c.

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    if( pList->a[j].iCursor==iCursor ) return pList->a[j].pTab;
  }
  return 0;
}


/*
** Generate code that will tell the VDBE the names of columns
** in the result set.  This information is used to provide the
** azCol[] values in the callback.

























*/
static void generateColumnNames(
  Parse *pParse,      /* Parser context */
  SrcList *pTabList,  /* List of tables */
  ExprList *pEList    /* Expressions defining the result set */
){
  Vdbe *v = pParse->pVdbe;
  int i;
  Table *pTab;
  sqlite3 *db = pParse->db;
  int fullNames, shortNames;


#ifndef SQLITE_OMIT_EXPLAIN
  /* If this is an EXPLAIN, skip this step */
  if( pParse->explain ){
    return;
  }
#endif

  if( pParse->colNamesSet || db->mallocFailed ) return;
  assert( v!=0 );
  assert( pTabList!=0 );
  pParse->colNamesSet = 1;
  fullNames = (db->flags & SQLITE_FullColNames)!=0;
  shortNames = (db->flags & SQLITE_ShortColNames)!=0;
  sqlite3VdbeSetNumCols(v, pEList->nExpr);
  for(i=0; i<pEList->nExpr; i++){
    Expr *p;
    p = pEList->a[i].pExpr;

    if( NEVER(p==0) ) continue;
    if( pEList->a[i].zName ){

      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)
           && (pTab = tableWithCursor(pTabList, p->iTable))!=0
    ){
      char *zCol;
      int iCol = p->iColumn;
      if( iCol<0 ) iCol = pTab->iPKey;
      assert( iCol==-1 || (iCol>=0 && iCol<pTab->nCol) );
      if( iCol<0 ){
        zCol = "rowid";
      }else{
        zCol = pTab->aCol[iCol].zName;
      }
      if( !shortNames && !fullNames ){
        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);
      }else{
        sqlite3VdbeSetColName(v, i, COLNAME_NAME, zCol, SQLITE_TRANSIENT);
      }
    }else{
................................................................................
** All column names will be unique.
**
** Only the column names are computed.  Column.zType, Column.zColl,
** and other fields of Column are zeroed.
**
** Return SQLITE_OK on success.  If a memory allocation error occurs,
** store NULL in *paCol and 0 in *pnCol and return SQLITE_NOMEM.









*/
int sqlite3ColumnsFromExprList(
  Parse *pParse,          /* Parsing context */
  ExprList *pEList,       /* Expr list from which to derive column names */
  i16 *pnCol,             /* Write the number of columns here */
  Column **paCol          /* Write the new column list here */
){
  sqlite3 *db = pParse->db;   /* Database connection */
  int i, j;                   /* Loop counters */
  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 */

  sqlite3HashInit(&ht);
  if( pEList ){
    nCol = pEList->nExpr;
................................................................................
  assert( nCol==(i16)nCol );
  *pnCol = nCol;
  *paCol = aCol;

  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 */
      Table *pTab;         /* Table associated with this expression */
      while( pColExpr->op==TK_DOT ){
        pColExpr = pColExpr->pRight;
        assert( pColExpr!=0 );
      }
      if( pColExpr->op==TK_COLUMN && pColExpr->pTab!=0 ){
        /* For columns use the column name name */
        int iCol = pColExpr->iColumn;
        pTab = pColExpr->pTab;
        if( iCol<0 ) iCol = pTab->iPKey;
        zName = iCol>=0 ? pTab->aCol[iCol].zName : "rowid";
      }else if( pColExpr->op==TK_ID ){
        assert( !ExprHasProperty(pColExpr, EP_IntValue) );
        zName = pColExpr->u.zToken;
      }else{
        /* Use the original text of the column expression as its name */







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    if( pList->a[j].iCursor==iCursor ) return pList->a[j].pTab;
  }
  return 0;
}


/*
** Compute the column names for a SELECT statement.
**
** 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,  /* 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 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 */
  if( pParse->explain ){
    return;
  }
#endif

  if( pParse->colNamesSet || db->mallocFailed ) return;
  assert( v!=0 );
  assert( pTabList!=0 );
  pParse->colNamesSet = 1;
  fullName = (db->flags & SQLITE_FullColNames)!=0;
  srcName = (db->flags & SQLITE_ShortColNames)!=0 || fullName;
  sqlite3VdbeSetNumCols(v, pEList->nExpr);
  for(i=0; i<pEList->nExpr; i++){

    Expr *p = pEList->a[i].pExpr;

    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( srcName
           && (p->op==TK_COLUMN || p->op==TK_AGG_COLUMN)
           && (pTab = tableWithCursor(pTabList, p->iTable))!=0
    ){
      char *zCol;
      int iCol = p->iColumn;
      if( iCol<0 ) iCol = pTab->iPKey;
      assert( iCol==-1 || (iCol>=0 && iCol<pTab->nCol) );
      if( iCol<0 ){
        zCol = "rowid";
      }else{
        zCol = pTab->aCol[iCol].zName;
      }



      if( fullName ){
        char *zName = 0;
        zName = sqlite3MPrintf(db, "%s.%s", pTab->zName, zCol);
        sqlite3VdbeSetColName(v, i, COLNAME_NAME, zName, SQLITE_DYNAMIC);
      }else{
        sqlite3VdbeSetColName(v, i, COLNAME_NAME, zCol, SQLITE_TRANSIENT);
      }
    }else{
................................................................................
** All column names will be unique.
**
** Only the column names are computed.  Column.zType, Column.zColl,
** and other fields of Column are zeroed.
**
** 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 */
  ExprList *pEList,       /* Expr list from which to derive column names */
  i16 *pnCol,             /* Write the number of columns here */
  Column **paCol          /* Write the new column list here */
){
  sqlite3 *db = pParse->db;   /* Database connection */
  int i, j;                   /* Loop counters */
  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 */

  char *zName;                /* Column name */
  int nName;                  /* Size of name in zName[] */
  Hash ht;                    /* Hash table of column names */

  sqlite3HashInit(&ht);
  if( pEList ){
    nCol = pEList->nExpr;
................................................................................
  assert( nCol==(i16)nCol );
  *pnCol = nCol;
  *paCol = aCol;

  for(i=0, pCol=aCol; i<nCol && !db->mallocFailed; i++, pCol++){
    /* Get an appropriate name for the column
    */

    if( (zName = pEList->a[i].zName)!=0 ){
      /* If the column contains an "AS <name>" phrase, use <name> as the name */
    }else{
      Expr *pColExpr = sqlite3ExprSkipCollate(pEList->a[i].pExpr);

      while( pColExpr->op==TK_DOT ){
        pColExpr = pColExpr->pRight;
        assert( pColExpr!=0 );
      }
      if( pColExpr->op==TK_COLUMN && pColExpr->pTab!=0 ){
        /* For columns use the column name name */
        int iCol = pColExpr->iColumn;
        Table *pTab = pColExpr->pTab;
        if( iCol<0 ) iCol = pTab->iPKey;
        zName = iCol>=0 ? pTab->aCol[iCol].zName : "rowid";
      }else if( pColExpr->op==TK_ID ){
        assert( !ExprHasProperty(pColExpr, EP_IntValue) );
        zName = pColExpr->u.zToken;
      }else{
        /* Use the original text of the column expression as its name */