}
    }
  }while( bMatch==0 );

  pNode->iRowid = iLast;
  return rc;
}








































/*
** Argument pNode points to a NEAR node. All individual term iterators 
** point to valid entries (not EOF).
*
** This function tests if the term iterators currently all point to the
** same rowid, and if so, if the row matches the phrase and NEAR constraints. 
................................................................................
** EOF.
*/
static int fts5ExprNearNextMatch(
  Fts5Expr *pExpr,                /* Expression that pNear is a part of */
  Fts5ExprNode *pNode             /* The "NEAR" node (FTS5_STRING) */
){
  Fts5ExprNearset *pNear = pNode->pNear;


  if( pNear->nPhrase==1 



   && pNear->apPhrase[0]->nTerm==1 
   && pNear->iCol<0
  ){
    /* If this "NEAR" object is actually a single phrase that consists of
    ** a single term only, then the row that it currently points to must
    ** be a match. All that is required is to populate pPhrase->poslist
    ** with the position-list data for the only term.  */


    Fts5ExprPhrase *pPhrase = pNear->apPhrase[0];
    Fts5IndexIter *pIter = pPhrase->aTerm[0].pIter;
    assert( pPhrase->poslist.nSpace==0 );
    return sqlite3Fts5IterPoslist(pIter, 
        (const u8**)&pPhrase->poslist.p, &pPhrase->poslist.n, &pNode->iRowid
    );
  }else{
    int rc = SQLITE_OK;

    while( 1 ){
      int i;














      /* Advance the iterators until they all point to the same rowid */
      rc = fts5ExprNearNextRowidMatch(pExpr, pNode);
      if( rc!=SQLITE_OK || pNode->bEof ) break;

      /* Check that each phrase in the nearset matches the current row.
      ** Populate the pPhrase->poslist buffers at the same time. If any
................................................................................
        if( pPhrase->nTerm>1 || pNear->iCol>=0 ){
          int bMatch = 0;
          rc = fts5ExprPhraseIsMatch(pExpr, pNear->iCol, pPhrase, &bMatch);
          if( bMatch==0 ) break;
        }else{
          rc = sqlite3Fts5IterPoslistBuffer(
              pPhrase->aTerm[0].pIter, &pPhrase->poslist
          );
        }
      }

      if( rc==SQLITE_OK && i==pNear->nPhrase ){
        int bMatch = 1;
        if( pNear->nPhrase>1 ){
          rc = fts5ExprNearIsMatch(pNear, &bMatch);
        }
        if( rc!=SQLITE_OK || bMatch ) break;
      }


      /* If control flows to here, then the current rowid is not a match.
      ** Advance all term iterators in all phrases to the next rowid. */
      if( rc==SQLITE_OK ){
        rc = fts5ExprNearAdvanceFirst(pExpr, pNode, 0, 0);
      }
      if( pNode->bEof || rc!=SQLITE_OK ) break;
    }

    return rc;
  }
}

/*
** Initialize all term iterators in the pNear object. If any term is found
** to match no documents at all, set *pbEof to true and return immediately,
** without initializing any further iterators.
*/

      }
    }
  }while( bMatch==0 );

  pNode->iRowid = iLast;
  return rc;
}

/*
** IN/OUT parameter (*pa) points to a position list n bytes in size. If
** the position list contains entries for column iCol, then (*pa) is set
** to point to the sub-position-list for that column and the number of
** bytes in it returned. Or, if the argument position list does not
** contain any entries for column iCol, return 0.
*/
static int fts5ExprExtractCol(
  const u8 **pa,                  /* IN/OUT: Pointer to poslist */
  int n,                          /* IN: Size of poslist in bytes */
  int iCol                        /* Column to extract from poslist */
){
  int ii;
  int iCurrent = 0;
  const u8 *p = *pa;
  const u8 *pEnd = &p[n];         /* One byte past end of position list */
  u8 prev = 0;

  while( iCol!=iCurrent ){
    /* Advance pointer p until it points to pEnd or an 0x01 byte that is
    ** not part of a varint */
    while( !(prev & 0x80) && *p!=0x01 ){
      prev = *p++;
      if( p==pEnd ) return 0;
    }
    *pa = p++;
    p += getVarint32(p, iCurrent);
  }

  /* Advance pointer p until it points to pEnd or an 0x01 byte that is
  ** not part of a varint */
  while( p<pEnd && !(prev & 0x80) && *p!=0x01 ){
    prev = *p++;
  }
  return p - (*pa);
}



/*
** Argument pNode points to a NEAR node. All individual term iterators 
** point to valid entries (not EOF).
*
** This function tests if the term iterators currently all point to the
** same rowid, and if so, if the row matches the phrase and NEAR constraints. 
................................................................................
** EOF.
*/
static int fts5ExprNearNextMatch(
  Fts5Expr *pExpr,                /* Expression that pNear is a part of */
  Fts5ExprNode *pNode             /* The "NEAR" node (FTS5_STRING) */
){
  Fts5ExprNearset *pNear = pNode->pNear;
  int rc = SQLITE_OK;


  while( 1 ){
    int i;

    if( pNear->nPhrase==1 && pNear->apPhrase[0]->nTerm==1 ){


      /* If this "NEAR" object is actually a single phrase that consists 
      ** of a single term only, then grab pointers into the poslist

      ** managed by the fts5_index.c iterator object. This is much faster 
      ** than synthesizing a new poslist the way we have to for more
      ** complicated phrase or NEAR expressions.  */
      Fts5ExprPhrase *pPhrase = pNear->apPhrase[0];
      Fts5IndexIter *pIter = pPhrase->aTerm[0].pIter;
      assert( pPhrase->poslist.nSpace==0 );
      rc = sqlite3Fts5IterPoslist(pIter, 
          (const u8**)&pPhrase->poslist.p, &pPhrase->poslist.n, &pNode->iRowid
      );



      /* If the term may match any column, then this must be a match. 
      ** Return immediately in this case. Otherwise, try to find the
      ** part of the poslist that corresponds to the required column.
      ** If it can be found, return. If it cannot, the next iteration
      ** of the loop will test the next rowid in the database for this
      ** term.  */
      if( pNear->iCol<0 ) return rc;

      pPhrase->poslist.n = fts5ExprExtractCol(
          (const u8**)&pPhrase->poslist.p,
          pPhrase->poslist.n,
          pNear->iCol
      );
      if( pPhrase->poslist.n ) return rc;
    }else{

      /* Advance the iterators until they all point to the same rowid */
      rc = fts5ExprNearNextRowidMatch(pExpr, pNode);
      if( rc!=SQLITE_OK || pNode->bEof ) break;

      /* Check that each phrase in the nearset matches the current row.
      ** Populate the pPhrase->poslist buffers at the same time. If any
................................................................................
        if( pPhrase->nTerm>1 || pNear->iCol>=0 ){
          int bMatch = 0;
          rc = fts5ExprPhraseIsMatch(pExpr, pNear->iCol, pPhrase, &bMatch);
          if( bMatch==0 ) break;
        }else{
          rc = sqlite3Fts5IterPoslistBuffer(
              pPhrase->aTerm[0].pIter, &pPhrase->poslist
              );
        }
      }

      if( rc==SQLITE_OK && i==pNear->nPhrase ){
        int bMatch = 1;
        if( pNear->nPhrase>1 ){
          rc = fts5ExprNearIsMatch(pNear, &bMatch);
        }
        if( rc!=SQLITE_OK || bMatch ) break;
      }
    }

    /* If control flows to here, then the current rowid is not a match.
    ** Advance all term iterators in all phrases to the next rowid. */
    if( rc==SQLITE_OK ){
      rc = fts5ExprNearAdvanceFirst(pExpr, pNode, 0, 0);
    }
    if( pNode->bEof || rc!=SQLITE_OK ) break;
  }

  return rc;

}

/*
** Initialize all term iterators in the pNear object. If any term is found
** to match no documents at all, set *pbEof to true and return immediately,
** without initializing any further iterators.
*/

  set res [list]
  db eval { SELECT * FROM b2 ORDER BY rowid ASC } {
    lappend res [execsql { SELECT * FROM b2 ORDER BY rowid ASC }]
  }
  set res
} {{a b c} {a b c} {a b c}}








finish_test

  set res [list]
  db eval { SELECT * FROM b2 ORDER BY rowid ASC } {
    lappend res [execsql { SELECT * FROM b2 ORDER BY rowid ASC }]
  }
  set res
} {{a b c} {a b c} {a b c}}

reset_db
do_execsql_test 18.1 {
  CREATE VIRTUAL TABLE c2 USING fts5(x, y);
  INSERT INTO c2 VALUES('x x x', 'x x x');
  SELECT rowid FROM c2 WHERE c2 MATCH 'y:x';
} {1}

finish_test