static int selectNodeIsConstant(Walker *pWalker, Select *NotUsed){
  UNUSED_PARAMETER(NotUsed);
  pWalker->u.i = 0;
  return WRC_Abort;
}
static int exprIsConst(Expr *p, int initFlag){
  Walker w;

  w.u.i = initFlag;
  w.xExprCallback = exprNodeIsConstant;
  w.xSelectCallback = selectNodeIsConstant;
  sqlite3WalkExpr(&w, p);
  return w.u.i;
}

................................................................................
** obtained for queries regardless of whether or not constants are
** precomputed into registers or if they are inserted in-line.
*/
void sqlite3ExprCodeConstants(Parse *pParse, Expr *pExpr){
  Walker w;
  if( pParse->cookieGoto ) return;
  if( OptimizationDisabled(pParse->db, SQLITE_FactorOutConst) ) return;

  w.xExprCallback = evalConstExpr;
  w.xSelectCallback = 0;
  w.pParse = pParse;
  sqlite3WalkExpr(&w, pExpr);
}


/*
** Generate code that pushes the value of every element of the given

static int selectNodeIsConstant(Walker *pWalker, Select *NotUsed){
  UNUSED_PARAMETER(NotUsed);
  pWalker->u.i = 0;
  return WRC_Abort;
}
static int exprIsConst(Expr *p, int initFlag){
  Walker w;
  memset(&w, 0, sizeof(w));
  w.u.i = initFlag;
  w.xExprCallback = exprNodeIsConstant;
  w.xSelectCallback = selectNodeIsConstant;
  sqlite3WalkExpr(&w, p);
  return w.u.i;
}

................................................................................
** obtained for queries regardless of whether or not constants are
** precomputed into registers or if they are inserted in-line.
*/
void sqlite3ExprCodeConstants(Parse *pParse, Expr *pExpr){
  Walker w;
  if( pParse->cookieGoto ) return;
  if( OptimizationDisabled(pParse->db, SQLITE_FactorOutConst) ) return;
  memset(&w, 0, sizeof(w));
  w.xExprCallback = evalConstExpr;

  w.pParse = pParse;
  sqlite3WalkExpr(&w, pExpr);
}


/*
** Generate code that pushes the value of every element of the given

      return 1;
    }
    pParse->nHeight += pExpr->nHeight;
  }
#endif
  savedHasAgg = pNC->ncFlags & NC_HasAgg;
  pNC->ncFlags &= ~NC_HasAgg;

  w.xExprCallback = resolveExprStep;
  w.xSelectCallback = resolveSelectStep;
  w.pParse = pNC->pParse;
  w.u.pNC = pNC;
  sqlite3WalkExpr(&w, pExpr);
#if SQLITE_MAX_EXPR_DEPTH>0
  pNC->pParse->nHeight -= pExpr->nHeight;
................................................................................
  Parse *pParse,         /* The parser context */
  Select *p,             /* The SELECT statement being coded. */
  NameContext *pOuterNC  /* Name context for parent SELECT statement */
){
  Walker w;

  assert( p!=0 );

  w.xExprCallback = resolveExprStep;
  w.xSelectCallback = resolveSelectStep;
  w.pParse = pParse;
  w.u.pNC = pOuterNC;
  sqlite3WalkSelect(&w, p);
}

      return 1;
    }
    pParse->nHeight += pExpr->nHeight;
  }
#endif
  savedHasAgg = pNC->ncFlags & NC_HasAgg;
  pNC->ncFlags &= ~NC_HasAgg;
  memset(&w, 0, sizeof(w));
  w.xExprCallback = resolveExprStep;
  w.xSelectCallback = resolveSelectStep;
  w.pParse = pNC->pParse;
  w.u.pNC = pNC;
  sqlite3WalkExpr(&w, pExpr);
#if SQLITE_MAX_EXPR_DEPTH>0
  pNC->pParse->nHeight -= pExpr->nHeight;
................................................................................
  Parse *pParse,         /* The parser context */
  Select *p,             /* The SELECT statement being coded. */
  NameContext *pOuterNC  /* Name context for parent SELECT statement */
){
  Walker w;

  assert( p!=0 );
  memset(&w, 0, sizeof(w));
  w.xExprCallback = resolveExprStep;
  w.xSelectCallback = resolveSelectStep;
  w.pParse = pParse;
  w.u.pNC = pOuterNC;
  sqlite3WalkSelect(&w, p);
}

**
** If anything goes wrong, an error message is written into pParse.
** The calling function can detect the problem by looking at pParse->nErr
** and/or pParse->db->mallocFailed.
*/
static void sqlite3SelectExpand(Parse *pParse, Select *pSelect){
  Walker w;

  w.xSelectCallback = selectExpander;
  w.xExprCallback = exprWalkNoop;
  w.pParse = pParse;
  sqlite3WalkSelect(&w, pSelect);
}


................................................................................
** SELECT statement.
**
** Use this routine after name resolution.
*/
static void sqlite3SelectAddTypeInfo(Parse *pParse, Select *pSelect){
#ifndef SQLITE_OMIT_SUBQUERY
  Walker w;

  w.xSelectCallback = selectAddSubqueryTypeInfo;
  w.xExprCallback = exprWalkNoop;
  w.pParse = pParse;

  sqlite3WalkSelect(&w, pSelect);
#endif
}


/*
** This routine sets up a SELECT statement for processing.  The

**
** If anything goes wrong, an error message is written into pParse.
** The calling function can detect the problem by looking at pParse->nErr
** and/or pParse->db->mallocFailed.
*/
static void sqlite3SelectExpand(Parse *pParse, Select *pSelect){
  Walker w;
  memset(&w, 0, sizeof(w));
  w.xSelectCallback = selectExpander;
  w.xExprCallback = exprWalkNoop;
  w.pParse = pParse;
  sqlite3WalkSelect(&w, pSelect);
}


................................................................................
** SELECT statement.
**
** Use this routine after name resolution.
*/
static void sqlite3SelectAddTypeInfo(Parse *pParse, Select *pSelect){
#ifndef SQLITE_OMIT_SUBQUERY
  Walker w;
  memset(&w, 0, sizeof(w));
  w.xSelectCallback = selectAddSubqueryTypeInfo;
  w.xExprCallback = exprWalkNoop;
  w.pParse = pParse;
  w.bSelectDepthFirst = 1;
  sqlite3WalkSelect(&w, pSelect);
#endif
}


/*
** This routine sets up a SELECT statement for processing.  The

** Context pointer passed down through the tree-walk.
*/
struct Walker {
  int (*xExprCallback)(Walker*, Expr*);     /* Callback for expressions */
  int (*xSelectCallback)(Walker*,Select*);  /* Callback for SELECTs */
  Parse *pParse;                            /* Parser context.  */
  int walkerDepth;                          /* Number of subqueries */

  union {                                   /* Extra data for callback */
    NameContext *pNC;                          /* Naming context */
    int i;                                     /* Integer value */
    SrcList *pSrcList;                         /* FROM clause */
    struct SrcCount *pSrcCount;                /* Counting column references */
  } u;
};

** Context pointer passed down through the tree-walk.
*/
struct Walker {
  int (*xExprCallback)(Walker*, Expr*);     /* Callback for expressions */
  int (*xSelectCallback)(Walker*,Select*);  /* Callback for SELECTs */
  Parse *pParse;                            /* Parser context.  */
  int walkerDepth;                          /* Number of subqueries */
  u8 bSelectDepthFirst;                     /* Do subqueries first */
  union {                                   /* Extra data for callback */
    NameContext *pNC;                          /* Naming context */
    int i;                                     /* Integer value */
    SrcList *pSrcList;                         /* FROM clause */
    struct SrcCount *pSrcCount;                /* Counting column references */
  } u;
};

  }
  return WRC_Continue;
} 

/*
** Call sqlite3WalkExpr() for every expression in Select statement p.
** Invoke sqlite3WalkSelect() for subqueries in the FROM clause and
** on the compound select chain, p->pPrior.


**
** Return WRC_Continue under normal conditions.  Return WRC_Abort if
** there is an abort request.
**
** If the Walker does not have an xSelectCallback() then this routine
** is a no-op returning WRC_Continue.
*/
int sqlite3WalkSelect(Walker *pWalker, Select *p){
  int rc;
  if( p==0 || pWalker->xSelectCallback==0 ) return WRC_Continue;
  rc = WRC_Continue;
  pWalker->walkerDepth++;
  while( p ){

    rc = pWalker->xSelectCallback(pWalker, p);
    if( rc ) break;

    if( sqlite3WalkSelectExpr(pWalker, p)
     || sqlite3WalkSelectFrom(pWalker, p)
    ){
      pWalker->walkerDepth--;
      return WRC_Abort;







    }
    p = p->pPrior;
  }
  pWalker->walkerDepth--;
  return rc & WRC_Abort;
}

  }
  return WRC_Continue;
} 

/*
** Call sqlite3WalkExpr() for every expression in Select statement p.
** Invoke sqlite3WalkSelect() for subqueries in the FROM clause and
** on the compound select chain, p->pPrior.  Invoke the xSelectCallback()
** either before or after the walk of expressions and FROM clause, depending
** on whether pWalker->bSelectDepthFirst is false or true, respectively.
**
** Return WRC_Continue under normal conditions.  Return WRC_Abort if
** there is an abort request.
**
** If the Walker does not have an xSelectCallback() then this routine
** is a no-op returning WRC_Continue.
*/
int sqlite3WalkSelect(Walker *pWalker, Select *p){
  int rc;
  if( p==0 || pWalker->xSelectCallback==0 ) return WRC_Continue;
  rc = WRC_Continue;
  pWalker->walkerDepth++;
  while( p ){
    if( !pWalker->bSelectDepthFirst ){
       rc = pWalker->xSelectCallback(pWalker, p);
       if( rc ) break;
    }
    if( sqlite3WalkSelectExpr(pWalker, p)
     || sqlite3WalkSelectFrom(pWalker, p)
    ){
      pWalker->walkerDepth--;
      return WRC_Abort;
    }
    if( pWalker->bSelectDepthFirst ){
      rc = pWalker->xSelectCallback(pWalker, p);
      /* Depth-first search is currently only used for
      ** selectAddSubqueryTypeInfo() and that routine always returns
      ** WRC_Continue (0).  So the following branch is never taken. */
      if( NEVER(rc) ) break;
    }
    p = p->pPrior;
  }
  pWalker->walkerDepth--;
  return rc & WRC_Abort;
}

    db eval {
      SELECT t1.*, t2.*, t3.*, t4.b
        FROM (t1 LEFT JOIN t2 USING(a)) JOIN (t3 LEFT JOIN t4 USING(a))
             ON t1.a=t3.a-111;
    }
  } {111 x1 111 x2 222 x3 {}}
}




















finish_test

    db eval {
      SELECT t1.*, t2.*, t3.*, t4.b
        FROM (t1 LEFT JOIN t2 USING(a)) JOIN (t3 LEFT JOIN t4 USING(a))
             ON t1.a=t3.a-111;
    }
  } {111 x1 111 x2 222 x3 {}}
}

# The following test was added on 2013-04-24 in order to verify that
# the datatypes and affinities of sub-sub-queries are set prior to computing
# the datatypes and affinities of the parent sub-queries because the 
# latter computation depends on the former.
#
do_execsql_test selectD-4.1 {
  CREATE TABLE t41(a INTEGER PRIMARY KEY, b INTEGER);
  CREATE TABLE t42(d INTEGER PRIMARY KEY, e INTEGER);
  CREATE TABLE t43(f INTEGER PRIMARY KEY, g INTEGER);
  EXPLAIN QUERY PLAN
  SELECT * 
   FROM t41
   LEFT JOIN (SELECT count(*) AS cnt, x1.d
                FROM (t42 INNER JOIN t43 ON d=g) AS x1
               WHERE x1.d>5
               GROUP BY x1.d) AS x2
                  ON t41.b=x2.d;
} {/.*SEARCH SUBQUERY 1 AS x2 USING AUTOMATIC.*/}

finish_test