sqlite3StrAccumAppendAll(pStr, zColumn);
  sqlite3StrAccumAppend(pStr, zOp, 1);
  sqlite3StrAccumAppend(pStr, "?", 1);
}

/*
** Argument pLevel describes a strategy for scanning table pTab. This 
** function returns a pointer to a string buffer containing a description
** of the subset of table rows scanned by the strategy in the form of an
** SQL expression. Or, if all rows are scanned, NULL is returned.
**
** For example, if the query:
**
**   SELECT * FROM t1 WHERE a=1 AND b>2;
**
** is run and there is an index on (a, b), then this function returns a
** string similar to:
**
**   "a=? AND b>?"
**
** The returned pointer points to memory obtained from sqlite3DbMalloc().
** It is the responsibility of the caller to free the buffer when it is
** no longer required.
*/
static char *explainIndexRange(sqlite3 *db, WhereLoop *pLoop, Table *pTab){
  Index *pIndex = pLoop->u.btree.pIndex;
  u16 nEq = pLoop->u.btree.nEq;
  u16 nSkip = pLoop->u.btree.nSkip;
  int i, j;
  Column *aCol = pTab->aCol;
  i16 *aiColumn = pIndex->aiColumn;
  StrAccum txt;

  if( nEq==0 && (pLoop->wsFlags & (WHERE_BTM_LIMIT|WHERE_TOP_LIMIT))==0 ){
    return 0;
  }
  sqlite3StrAccumInit(&txt, 0, 0, SQLITE_MAX_LENGTH);
  txt.db = db;
  sqlite3StrAccumAppend(&txt, " (", 2);
  for(i=0; i<nEq; i++){
    char *z = aiColumn[i] < 0 ? "rowid" : aCol[aiColumn[i]].zName;
    if( i>=nSkip ){
      explainAppendTerm(&txt, i, z, "=");
    }else{
      if( i ) sqlite3StrAccumAppend(&txt, " AND ", 5);
      sqlite3StrAccumAppend(&txt, "ANY(", 4);
      sqlite3StrAccumAppendAll(&txt, z);
      sqlite3StrAccumAppend(&txt, ")", 1);
    }
  }

  j = i;
  if( pLoop->wsFlags&WHERE_BTM_LIMIT ){
    char *z = aiColumn[j] < 0 ? "rowid" : aCol[aiColumn[j]].zName;
    explainAppendTerm(&txt, i++, z, ">");
  }
  if( pLoop->wsFlags&WHERE_TOP_LIMIT ){
    char *z = aiColumn[j] < 0 ? "rowid" : aCol[aiColumn[j]].zName;
    explainAppendTerm(&txt, i, z, "<");
  }
  sqlite3StrAccumAppend(&txt, ")", 1);
  return sqlite3StrAccumFinish(&txt);
}

/*
** This function is a no-op unless currently processing an EXPLAIN QUERY PLAN
** command. If the query being compiled is an EXPLAIN QUERY PLAN, a single
** record is added to the output to describe the table scan strategy in 
** pLevel.
................................................................................
#ifndef SQLITE_DEBUG
  if( pParse->explain==2 )
#endif
  {
    struct SrcList_item *pItem = &pTabList->a[pLevel->iFrom];
    Vdbe *v = pParse->pVdbe;      /* VM being constructed */
    sqlite3 *db = pParse->db;     /* Database handle */
    char *zMsg;                   /* Text to add to EQP output */
    int iId = pParse->iSelectId;  /* Select id (left-most output column) */
    int isSearch;                 /* True for a SEARCH. False for SCAN. */
    WhereLoop *pLoop;             /* The controlling WhereLoop object */
    u32 flags;                    /* Flags that describe this loop */




    pLoop = pLevel->pWLoop;
    flags = pLoop->wsFlags;
    if( (flags&WHERE_MULTI_OR) || (wctrlFlags&WHERE_ONETABLE_ONLY) ) return;

    isSearch = (flags&(WHERE_BTM_LIMIT|WHERE_TOP_LIMIT))!=0
            || ((flags&WHERE_VIRTUALTABLE)==0 && (pLoop->u.btree.nEq>0))
            || (wctrlFlags&(WHERE_ORDERBY_MIN|WHERE_ORDERBY_MAX));

    zMsg = sqlite3MPrintf(db, "%s", isSearch?"SEARCH":"SCAN");


    if( pItem->pSelect ){
      zMsg = sqlite3MAppendf(db, zMsg, "%s SUBQUERY %d", zMsg,pItem->iSelectId);

    }else{
      zMsg = sqlite3MAppendf(db, zMsg, "%s TABLE %s", zMsg, pItem->zName);

    }

    if( pItem->zAlias ){
      zMsg = sqlite3MAppendf(db, zMsg, "%s AS %s", zMsg, pItem->zAlias);
    }
    if( (flags & (WHERE_IPK|WHERE_VIRTUALTABLE))==0
     && ALWAYS(pLoop->u.btree.pIndex!=0)
    ){
      const char *zFmt;



      Index *pIdx = pLoop->u.btree.pIndex;
      char *zWhere = explainIndexRange(db, pLoop, pItem->pTab);
      assert( !(flags&WHERE_AUTO_INDEX) || (flags&WHERE_IDX_ONLY) );
      if( !HasRowid(pItem->pTab) && IsPrimaryKeyIndex(pIdx) ){
        zFmt = zWhere ? "%s USING PRIMARY KEY%.0s%s" : "%s%.0s%s";




      }else if( flags & WHERE_AUTO_INDEX ){
        zFmt = "%s USING AUTOMATIC COVERING INDEX%.0s%s";
      }else if( flags & WHERE_IDX_ONLY ){
        zFmt = "%s USING COVERING INDEX %s%s";
      }else{
        zFmt = "%s USING INDEX %s%s";

      }
      zMsg = sqlite3MAppendf(db, zMsg, zFmt, zMsg, pIdx->zName, zWhere);
      sqlite3DbFree(db, zWhere);
    }else if( (flags & WHERE_IPK)!=0 && (flags & WHERE_CONSTRAINT)!=0 ){
      zMsg = sqlite3MAppendf(db, zMsg, "%s USING INTEGER PRIMARY KEY", zMsg);







      if( flags&(WHERE_COLUMN_EQ|WHERE_COLUMN_IN) ){
        zMsg = sqlite3MAppendf(db, zMsg, "%s (rowid=?)", zMsg);

      }else if( (flags&WHERE_BOTH_LIMIT)==WHERE_BOTH_LIMIT ){
        zMsg = sqlite3MAppendf(db, zMsg, "%s (rowid>? AND rowid<?)", zMsg);
      }else if( flags&WHERE_BTM_LIMIT ){
        zMsg = sqlite3MAppendf(db, zMsg, "%s (rowid>?)", zMsg);


      }else if( ALWAYS(flags&WHERE_TOP_LIMIT) ){
        zMsg = sqlite3MAppendf(db, zMsg, "%s (rowid<?)", zMsg);

      }


    }
#ifndef SQLITE_OMIT_VIRTUALTABLE
    else if( (flags & WHERE_VIRTUALTABLE)!=0 ){
      zMsg = sqlite3MAppendf(db, zMsg, "%s VIRTUAL TABLE INDEX %d:%s", zMsg,
                  pLoop->u.vtab.idxNum, pLoop->u.vtab.idxStr);
    }
#endif
    zMsg = sqlite3MAppendf(db, zMsg, "%s", zMsg);
    sqlite3VdbeAddOp4(v, OP_Explain, iId, iLevel, iFrom, zMsg, P4_DYNAMIC);
  }
}
#else
# define explainOneScan(u,v,w,x,y,z)
#endif /* SQLITE_OMIT_EXPLAIN */

  sqlite3StrAccumAppendAll(pStr, zColumn);
  sqlite3StrAccumAppend(pStr, zOp, 1);
  sqlite3StrAccumAppend(pStr, "?", 1);
}

/*
** Argument pLevel describes a strategy for scanning table pTab. This 
** function appends text to pStr that describes the subset of table
** rows scanned by the strategy in the form of an SQL expression.

**
** For example, if the query:
**
**   SELECT * FROM t1 WHERE a=1 AND b>2;
**
** is run and there is an index on (a, b), then this function returns a
** string similar to:
**
**   "a=? AND b>?"




*/
void explainIndexRange(StrAccum *pStr, WhereLoop *pLoop, Table *pTab){
  Index *pIndex = pLoop->u.btree.pIndex;
  u16 nEq = pLoop->u.btree.nEq;
  u16 nSkip = pLoop->u.btree.nSkip;
  int i, j;
  Column *aCol = pTab->aCol;
  i16 *aiColumn = pIndex->aiColumn;


  if( nEq==0 && (pLoop->wsFlags&(WHERE_BTM_LIMIT|WHERE_TOP_LIMIT))==0 ) return;




  sqlite3StrAccumAppend(pStr, " (", 2);
  for(i=0; i<nEq; i++){
    char *z = aiColumn[i] < 0 ? "rowid" : aCol[aiColumn[i]].zName;
    if( i>=nSkip ){
      explainAppendTerm(pStr, i, z, "=");
    }else{
      if( i ) sqlite3StrAccumAppend(pStr, " AND ", 5);
      sqlite3XPrintf(pStr, 0, "ANY(%s)", z);


    }
  }

  j = i;
  if( pLoop->wsFlags&WHERE_BTM_LIMIT ){
    char *z = aiColumn[j] < 0 ? "rowid" : aCol[aiColumn[j]].zName;
    explainAppendTerm(pStr, i++, z, ">");
  }
  if( pLoop->wsFlags&WHERE_TOP_LIMIT ){
    char *z = aiColumn[j] < 0 ? "rowid" : aCol[aiColumn[j]].zName;
    explainAppendTerm(pStr, i, z, "<");
  }
  sqlite3StrAccumAppend(pStr, ")", 1);

}

/*
** This function is a no-op unless currently processing an EXPLAIN QUERY PLAN
** command. If the query being compiled is an EXPLAIN QUERY PLAN, a single
** record is added to the output to describe the table scan strategy in 
** pLevel.
................................................................................
#ifndef SQLITE_DEBUG
  if( pParse->explain==2 )
#endif
  {
    struct SrcList_item *pItem = &pTabList->a[pLevel->iFrom];
    Vdbe *v = pParse->pVdbe;      /* VM being constructed */
    sqlite3 *db = pParse->db;     /* Database handle */

    int iId = pParse->iSelectId;  /* Select id (left-most output column) */
    int isSearch;                 /* True for a SEARCH. False for SCAN. */
    WhereLoop *pLoop;             /* The controlling WhereLoop object */
    u32 flags;                    /* Flags that describe this loop */
    char *zMsg;                   /* Text to add to EQP output */
    StrAccum str;                 /* EQP output string */
    char zBuf[100];               /* Initial space for EQP output string */

    pLoop = pLevel->pWLoop;
    flags = pLoop->wsFlags;
    if( (flags&WHERE_MULTI_OR) || (wctrlFlags&WHERE_ONETABLE_ONLY) ) return;

    isSearch = (flags&(WHERE_BTM_LIMIT|WHERE_TOP_LIMIT))!=0
            || ((flags&WHERE_VIRTUALTABLE)==0 && (pLoop->u.btree.nEq>0))
            || (wctrlFlags&(WHERE_ORDERBY_MIN|WHERE_ORDERBY_MAX));

    sqlite3StrAccumInit(&str, zBuf, sizeof(zBuf), SQLITE_MAX_LENGTH);
    str.db = db;
    sqlite3StrAccumAppendAll(&str, isSearch ? "SEARCH" : "SCAN");
    if( pItem->pSelect ){

      sqlite3XPrintf(&str, 0, " SUBQUERY %d", pItem->iSelectId);
    }else{

      sqlite3XPrintf(&str, 0, " TABLE %s", pItem->zName);
    }

    if( pItem->zAlias ){
      sqlite3XPrintf(&str, 0, " AS %s", pItem->zAlias);
    }
    if( (flags & (WHERE_IPK|WHERE_VIRTUALTABLE))==0 ){


      const char *zFmt = 0;
      Index *pIdx;

      assert( pLoop->u.btree.pIndex!=0 );
      pIdx = pLoop->u.btree.pIndex;

      assert( !(flags&WHERE_AUTO_INDEX) || (flags&WHERE_IDX_ONLY) );
      if( !HasRowid(pItem->pTab) && IsPrimaryKeyIndex(pIdx) ){
        if( pLoop->u.btree.nEq>0
         || (pLoop->wsFlags & (WHERE_BTM_LIMIT|WHERE_TOP_LIMIT))!=0
        ){
          zFmt = "PRIMARY KEY";
        }
      }else if( flags & WHERE_AUTO_INDEX ){
        zFmt = "AUTOMATIC COVERING INDEX";
      }else if( flags & WHERE_IDX_ONLY ){
        zFmt = "COVERING INDEX %s";
      }else{

        zFmt = "INDEX %s";
      }




      if( zFmt ){
        sqlite3StrAccumAppend(&str, " USING ", 7);
        sqlite3XPrintf(&str, 0, zFmt, pIdx->zName);
        explainIndexRange(&str, pLoop, pItem->pTab);
      }
    }else if( (flags & WHERE_IPK)!=0 && (flags & WHERE_CONSTRAINT)!=0 ){
      const char *zRange;
      if( flags&(WHERE_COLUMN_EQ|WHERE_COLUMN_IN) ){

        zRange = "(rowid=?)";
      }else if( (flags&WHERE_BOTH_LIMIT)==WHERE_BOTH_LIMIT ){
        zRange = "(rowid>? AND rowid<?)";
      }else if( flags&WHERE_BTM_LIMIT ){

        zRange = "(rowid>?)";
      }else{
        assert( flags&WHERE_TOP_LIMIT);

        zRange = "(rowid<?)";
      }
      sqlite3StrAccumAppendAll(&str, " USING INTEGER PRIMARY KEY ");
      sqlite3StrAccumAppendAll(&str, zRange);
    }
#ifndef SQLITE_OMIT_VIRTUALTABLE
    else if( (flags & WHERE_VIRTUALTABLE)!=0 ){
      sqlite3XPrintf(&str, 0, " VIRTUAL TABLE INDEX %d:%s",
                  pLoop->u.vtab.idxNum, pLoop->u.vtab.idxStr);
    }
#endif
    zMsg = sqlite3StrAccumFinish(&str);
    sqlite3VdbeAddOp4(v, OP_Explain, iId, iLevel, iFrom, zMsg, P4_DYNAMIC);
  }
}
#else
# define explainOneScan(u,v,w,x,y,z)
#endif /* SQLITE_OMIT_EXPLAIN */