SQLite

**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains C code routines that are called by the parser
** to handle SELECT statements in SQLite.
**
** $Id: select.c,v 1.391 2008/01/07 10:16:41 danielk1977 Exp $
*/
#include "sqliteInt.h"


/*
** Delete all the content of a Select structure but do not deallocate
** the select structure itself.

/*
** Analyze the SELECT statement passed as an argument to see if it
** is a min() or max() query. Return ORDERBY_MIN or ORDERBY_MAX if 
** it is, or 0 otherwise. At present, a query is considered to be
** a min()/max() query if:
**
**   1. There is a single object in the FROM clause.
**
**   2. There is a single expression in the result set, and it is
**      either min(x) or max(x), where x is a column reference.
*/
static int minMaxQuery(Parse *pParse, Select *p){
  Expr *pExpr;
  ExprList *pEList = p->pEList;

  if( pEList->nExpr!=1 ) return ORDERBY_NORMAL;
  pExpr = pEList->a[0].pExpr;

      
    } /* endif pGroupBy */
    else {
      ExprList *pMinMax = 0;
      ExprList *pDel = 0;
      u8 flag;

      /* Check if the query is of one of the following forms:
      **
      **   SELECT min(x) FROM ...
      **   SELECT max(x) FROM ...
      **
      ** If it is, then ask the code in where.c to attempt to sort results
      ** as if there was an "ORDER ON x" or "ORDER ON x DESC" clause. 
      ** If where.c is able to produce results sorted in this order, then
      ** add vdbe code to break out of the processing loop after the 
      ** first iteration (since the first iteration of the loop is 
      ** guaranteed to operate on the row with the minimum or maximum 
      ** value of x, the only row required).
      **
      ** A special flag must be passed to sqlite3WhereBegin() to slightly
      ** modify behaviour as follows:
      **
      **   + If the query is a "SELECT min(x)", then the loop coded by
      **     where.c should not iterate over any values with a NULL value
      **     for x.
      **
      **   + The optimizer code in where.c (the thing that decides which
      **     index or indices to use) should place a different priority on 
      **     satisfying the 'ORDER BY' clause than it does in other cases.
      **     Refer to code and comments in where.c for details.
      */
      flag = minMaxQuery(pParse, p);
      if( flag ){
        pMinMax = sqlite3ExprListDup(db, p->pEList->a[0].pExpr->pList);
        if( pMinMax ){
          pMinMax->a[0].sortOrder = ((flag==ORDERBY_MIN)?0:1);
          pMinMax->a[0].pExpr->op = TK_COLUMN;
          pDel = pMinMax;