SQLite

** for additional information.
*/
static int analyzeAggregate(Walker *pWalker, Expr *pExpr){
  int i;
  NameContext *pNC = pWalker->u.pNC;
  Parse *pParse = pNC->pParse;
  SrcList *pSrcList = pNC->pSrcList;
  AggInfo *pAggInfo = pNC->uNC.pAggInfo;

  assert( pNC->ncFlags & NC_UAggInfo );
  switch( pExpr->op ){
    case TK_AGG_COLUMN:
    case TK_COLUMN: {
      testcase( pExpr->op==TK_AGG_COLUMN );
      testcase( pExpr->op==TK_COLUMN );
      /* Check to see if the column is in one of the tables in the FROM
      ** clause of the aggregate query */

    **
    ** The ability to use an output result-set column in the WHERE, GROUP BY,
    ** or HAVING clauses, or as part of a larger expression in the ORDER BY
    ** clause is not standard SQL.  This is a (goofy) SQLite extension, that
    ** is supported for backwards compatibility only. Hence, we issue a warning
    ** on sqlite3_log() whenever the capability is used.
    */
    if( (pNC->ncFlags & NC_UEList)!=0

     && cnt==0
     && zTab==0
    ){
      pEList = pNC->uNC.pEList;
      assert( pEList!=0 );
      for(j=0; j<pEList->nExpr; j++){
        char *zAs = pEList->a[j].zName;
        if( zAs!=0 && sqlite3StrICmp(zAs, zCol)==0 ){
          Expr *pOrig;
          assert( pExpr->pLeft==0 && pExpr->pRight==0 );
          assert( pExpr->x.pList==0 );
          assert( pExpr->x.pSelect==0 );

  pEList = pSelect->pEList;

  /* Resolve all names in the ORDER BY term expression
  */
  memset(&nc, 0, sizeof(nc));
  nc.pParse = pParse;
  nc.pSrcList = pSelect->pSrc;
  nc.uNC.pEList = pEList;
  nc.ncFlags = NC_AllowAgg|NC_UEList;
  nc.nErr = 0;
  db = pParse->db;
  savedSuppErr = db->suppressErr;
  db->suppressErr = 1;
  rc = sqlite3ResolveExprNames(&nc, pE);
  db->suppressErr = savedSuppErr;
  if( rc ) return 0;

    ** other expressions in the SELECT statement. This is so that
    ** expressions in the WHERE clause (etc.) can refer to expressions by
    ** aliases in the result set.
    **
    ** Minor point: If this is the case, then the expression will be
    ** re-evaluated for each reference to it.
    */
    assert( (sNC.ncFlags & (NC_UAggInfo))==0 );
    sNC.uNC.pEList = p->pEList;
    sNC.ncFlags |= NC_UEList;
    if( sqlite3ResolveExprNames(&sNC, p->pHaving) ) return WRC_Abort;
    if( sqlite3ResolveExprNames(&sNC, p->pWhere) ) return WRC_Abort;

    /* Resolve names in table-valued-function arguments */
    for(i=0; i<p->pSrc->nSrc; i++){
      struct SrcList_item *pItem = &p->pSrc->a[i];
      if( pItem->fg.isTabFunc

    /* Convert TK_COLUMN nodes into TK_AGG_COLUMN and make entries in
    ** sAggInfo for all TK_AGG_FUNCTION nodes in expressions of the
    ** SELECT statement.
    */
    memset(&sNC, 0, sizeof(sNC));
    sNC.pParse = pParse;
    sNC.pSrcList = pTabList;
    sNC.uNC.pAggInfo = &sAggInfo;
    VVA_ONLY( sNC.ncFlags = NC_UAggInfo; )
    sAggInfo.mnReg = pParse->nMem+1;
    sAggInfo.nSortingColumn = pGroupBy ? pGroupBy->nExpr : 0;
    sAggInfo.pGroupBy = pGroupBy;
    sqlite3ExprAnalyzeAggList(&sNC, pEList);
    sqlite3ExprAnalyzeAggList(&sNC, sSort.pOrderBy);
    if( pHaving ){
      if( pGroupBy ){

** NameContext in the parent query.  Thus the process of scanning the
** NameContext list corresponds to searching through successively outer
** subqueries looking for a match.
*/
struct NameContext {
  Parse *pParse;       /* The parser */
  SrcList *pSrcList;   /* One or more tables used to resolve names */
  union {
    ExprList *pEList;    /* Optional list of result-set columns */
    AggInfo *pAggInfo;   /* Information about aggregates at this level */
  } uNC;
  NameContext *pNext;  /* Next outer name context.  NULL for outermost */
  int nRef;            /* Number of names resolved by this context */
  int nErr;            /* Number of errors encountered while resolving names */
  u16 ncFlags;         /* Zero or more NC_* flags defined below */
};

/*

#define NC_AllowAgg  0x0001  /* Aggregate functions are allowed here */
#define NC_PartIdx   0x0002  /* True if resolving a partial index WHERE */
#define NC_IsCheck   0x0004  /* True if resolving names in a CHECK constraint */
#define NC_InAggFunc 0x0008  /* True if analyzing arguments to an agg func */
#define NC_HasAgg    0x0010  /* One or more aggregate functions seen */
#define NC_IdxExpr   0x0020  /* True if resolving columns of CREATE INDEX */
#define NC_VarSelect 0x0040  /* A correlated subquery has been seen */
#define NC_UEList    0x0080  /* True if uNC.pEList is used */
#define NC_UAggInfo  0x0100  /* True if uNC.pAggInfo is used */
#define NC_MinMaxAgg 0x1000  /* min/max aggregates seen.  See note above */
#define NC_Complex   0x2000  /* True if a function or subquery seen */

/*
** An instance of the following structure contains all information
** needed to generate code for a single SELECT statement.
**