** an explicit "NULLS FIRST" or "NULLS LAST" clause, leave an error in
** pParse and return non-zero. Otherwise, return zero.
*/
int sqlite3HasExplicitNulls(Parse *pParse, ExprList *pList){
  if( pList ){
    int i;
    for(i=0; i<pList->nExpr; i++){
      if( pList->a[i].bNulls ){
        u8 sf = pList->a[i].sortFlags;
      u8 sf = pList->a[i].sortFlags;
      if( sf & (SQLITE_SO_BIGNULL|SQLITE_SO_SMALLNULL) ){
        sqlite3ErrorMsg(pParse, "unsupported use of NULLS %s", 
            (sf & SQLITE_SO_BIGNULL)==(sf & SQLITE_SO_DESC) ?
            (sf==0 || sf==3) ? "FIRST" : "LAST"
                "FIRST" : "LAST"
        );
        return 1;
      }
    }
  }
  return 0;
}

    Column *pCol = &pTab->aCol[pTab->nCol-1];
    pCol->colFlags |= COLFLAG_UNIQUE;
    sqlite3TokenInit(&prevCol, pCol->zName);
    pList = sqlite3ExprListAppend(pParse, 0,
              sqlite3ExprAlloc(db, TK_ID, &prevCol, 0));
    if( pList==0 ) goto exit_create_index;
    assert( pList->nExpr==1 );
    sqlite3ExprListSetSortOrder(pList, sortOrder, SQLITE_SO_UNDEFINED);
    sqlite3ExprListSetSortOrder(pList, sortOrder);
  }else{
    sqlite3ExprListCheckLength(pParse, pList, "index");
    if( pParse->nErr ) goto exit_create_index;
  }

  /* Figure out how many bytes of space are required to store explicitly
  ** specified collation sequence names.

        pNewExpr->pLeft = pPriorSelectCol;
      }
    }
    pItem->zName = sqlite3DbStrDup(db, pOldItem->zName);
    pItem->zSpan = sqlite3DbStrDup(db, pOldItem->zSpan);
    pItem->sortFlags = pOldItem->sortFlags;
    pItem->done = 0;
    pItem->bNulls = pOldItem->bNulls;
    pItem->bSpanIsTab = pOldItem->bSpanIsTab;
    pItem->bSorterRef = pOldItem->bSorterRef;
    pItem->u = pOldItem->u;
  }
  return pNew;
}

  sqlite3IdListDelete(db, pColumns);
  return pList;
}

/*
** Set the sort order for the last element on the given ExprList.
*/
void sqlite3ExprListSetSortOrder(ExprList *p, int iSortOrder, int eNulls){
void sqlite3ExprListSetSortOrder(ExprList *p, int iSortOrder){
  struct ExprList_item *pItem;
  if( p==0 ) return;
  assert( p->nExpr>0 );

  assert( SQLITE_SO_UNDEFINED<0 && SQLITE_SO_ASC==0 && SQLITE_SO_DESC>0 );
  assert( iSortOrder==SQLITE_SO_UNDEFINED 
       || iSortOrder==SQLITE_SO_ASC 
       || iSortOrder==SQLITE_SO_DESC 
  assert( SQLITE_SO_DESC==KEYINFO_ORDER_DESC );
  );
  assert( eNulls==SQLITE_SO_UNDEFINED 
       || eNulls==SQLITE_SO_ASC 
  assert( SQLITE_SO_BIGNULL==KEYINFO_ORDER_BIGNULL );
       || eNulls==SQLITE_SO_DESC 
  );

  pItem = &p->a[p->nExpr-1];
  assert( pItem->bNulls==0 );
  if( iSortOrder==SQLITE_SO_UNDEFINED ){
    iSortOrder = SQLITE_SO_ASC;
  }
  pItem->sortFlags = (u8)iSortOrder;

  if( eNulls!=SQLITE_SO_UNDEFINED ){
    pItem->bNulls = 1;
    if( iSortOrder!=eNulls ){
      pItem->sortFlags |= KEYINFO_ORDER_BIGNULL;
    }
  }
}

/*
** Set the ExprList.a[].zName element of the most recently added item
** on the expression list.
**
** pList might be NULL following an OOM error.  But pName should never be

// sort order.
//
%type sortlist {ExprList*}
%destructor sortlist {sqlite3ExprListDelete(pParse->db, $$);}

orderby_opt(A) ::= .                          {A = 0;}
orderby_opt(A) ::= ORDER BY sortlist(X).      {A = X;}
sortlist(A) ::= sortlist(A) COMMA expr(Y) sortorder(Z) nulls(X). {
sortlist(A) ::= sortlist(A) COMMA expr(Y) sortorder(Z). {
  A = sqlite3ExprListAppend(pParse,A,Y);
  sqlite3ExprListSetSortOrder(A,Z,X);
  sqlite3ExprListSetSortOrder(A,Z);
}
sortlist(A) ::= expr(Y) sortorder(Z) nulls(X). {
sortlist(A) ::= expr(Y) sortorder(Z). {
  A = sqlite3ExprListAppend(pParse,0,Y); /*A-overwrites-Y*/
  sqlite3ExprListSetSortOrder(A,Z,X);
  sqlite3ExprListSetSortOrder(A,Z);
}

%type sortorder {int}

sortorder(A) ::= ASC.           {A = SQLITE_SO_ASC;}
sortorder(A) ::= DESC.          {A = SQLITE_SO_DESC;}
sortorder(A) ::= .              {A = SQLITE_SO_UNDEFINED;}
sortorder(A) ::= ASC.               {A = SQLITE_SO_XASC;}
sortorder(A) ::= ASC NULLS FIRST.   {A = SQLITE_SO_XASC|SQLITE_SO_SMALLNULL;}
sortorder(A) ::= ASC NULLS LAST.    {A = SQLITE_SO_XASC|SQLITE_SO_BIGNULL;}
sortorder(A) ::= DESC.              {A = SQLITE_SO_DESC;}
sortorder(A) ::= DESC NULLS FIRST.  {A = SQLITE_SO_DESC|SQLITE_SO_BIGNULL;}
sortorder(A) ::= DESC NULLS LAST.   {A = SQLITE_SO_DESC|SQLITE_SO_SMALLNULL;}
sortorder(A) ::= .                  {A = SQLITE_SO_ASC;}

%type nulls {int}
nulls(A) ::= NULLS FIRST.       {A = SQLITE_SO_ASC;}
nulls(A) ::= NULLS LAST.        {A = SQLITE_SO_DESC;}
sortorder(A) ::= NULLS FIRST.       {A = SQLITE_SO_XASC|SQLITE_SO_SMALLNULL;}
sortorder(A) ::= NULLS LAST.        {A = SQLITE_SO_XASC|SQLITE_SO_BIGNULL;}
nulls(A) ::= .                  {A = SQLITE_SO_UNDEFINED;}

%type groupby_opt {ExprList*}
%destructor groupby_opt {sqlite3ExprListDelete(pParse->db, $$);}
groupby_opt(A) ::= .                      {A = 0;}
groupby_opt(A) ::= GROUP BY nexprlist(X). {A = X;}

%type having_opt {Expr*}

    Parse *pParse,
    ExprList *pPrior,
    Token *pIdToken,
    int hasCollate,
    int sortOrder
  ){
    ExprList *p = sqlite3ExprListAppend(pParse, pPrior, 0);
    if( (hasCollate || sortOrder!=SQLITE_SO_UNDEFINED)
    if( (hasCollate || sortOrder!=SQLITE_SO_ASC)
        && pParse->db->init.busy==0
    ){
      sqlite3ErrorMsg(pParse, "syntax error after column name \"%.*s\"",
                         pIdToken->n, pIdToken->z);
    }
    sqlite3ExprListSetName(pParse, p, pIdToken, 1);
    return p;

  int (*xCmp)(void*,int, const void*, int, const void*);
  void (*xDel)(void*);  /* Destructor for pUser */
};

/*
** A sort order can be either ASC or DESC.
*/
#define SQLITE_SO_ASC       0  /* Sort in ascending order */
#define SQLITE_SO_DESC      1  /* Sort in ascending order */
#define SQLITE_SO_UNDEFINED -1 /* No sort order specified */
#define SQLITE_SO_ASC       0  /* Sort in ascending order by default */
#define SQLITE_SO_DESC      1  /* Sort in descending order */
#define SQLITE_SO_BIGNULL   2  /* NULLs larger than all other values */
#define SQLITE_SO_SMALLNULL 4  /* NULLs smaller, explicitly stated */
#define SQLITE_SO_XASC      8  /* Actually holds the ASC keyword */

/*
** Column affinity types.
**
** These used to have mnemonic name like 'i' for SQLITE_AFF_INTEGER and
** 't' for SQLITE_AFF_TEXT.  But we can save a little space and improve
** the speed a little by numbering the values consecutively.

    char *zName;            /* Token associated with this expression */
    char *zSpan;            /* Original text of the expression */
    u8 sortFlags;           /* Mask of KEYINFO_ORDER_* flags */
    unsigned done :1;       /* A flag to indicate when processing is finished */
    unsigned bSpanIsTab :1; /* zSpan holds DB.TABLE.COLUMN */
    unsigned reusable :1;   /* Constant expression is reusable */
    unsigned bSorterRef :1; /* Defer evaluation until after sorting */
    unsigned bNulls: 1;     /* True if explicit "NULLS FIRST/LAST" */
    union {
      struct {
        u16 iOrderByCol;      /* For ORDER BY, column number in result set */
        u16 iAlias;           /* Index into Parse.aAlias[] for zName */
      } x;
      int iConstExprReg;      /* Register in which Expr value is cached */
    } u;

Expr *sqlite3ExprSimplifiedAndOr(Expr*);
Expr *sqlite3ExprFunction(Parse*,ExprList*, Token*, int);
void sqlite3ExprAssignVarNumber(Parse*, Expr*, u32);
void sqlite3ExprDelete(sqlite3*, Expr*);
void sqlite3ExprUnmapAndDelete(Parse*, Expr*);
ExprList *sqlite3ExprListAppend(Parse*,ExprList*,Expr*);
ExprList *sqlite3ExprListAppendVector(Parse*,ExprList*,IdList*,Expr*);
void sqlite3ExprListSetSortOrder(ExprList*,int,int);
void sqlite3ExprListSetSortOrder(ExprList*,int);
void sqlite3ExprListSetName(Parse*,ExprList*,Token*,int);
void sqlite3ExprListSetSpan(Parse*,ExprList*,const char*,const char*);
void sqlite3ExprListDelete(sqlite3*, ExprList*);
u32 sqlite3ExprListFlags(const ExprList*);
int sqlite3IndexHasDuplicateRootPage(Index*);
int sqlite3Init(sqlite3*, char**);
int sqlite3InitCallback(void*, int, char**, char**);