SQLite

  ExpertVtab *p = (ExpertVtab*)pVtab;
  sqlite3_free(p);
  return SQLITE_OK;
}

static int expertBestIndex(sqlite3_vtab *pVtab, sqlite3_index_info *pIdxInfo){
  ExpertVtab *p = (ExpertVtab*)pVtab;

  int rc = SQLITE_OK;
  int n = 0;
  IdxScan *pScan;
  const int opmask = 
    SQLITE_INDEX_CONSTRAINT_EQ | SQLITE_INDEX_CONSTRAINT_GT |
    SQLITE_INDEX_CONSTRAINT_LT | SQLITE_INDEX_CONSTRAINT_GE |
    SQLITE_INDEX_CONSTRAINT_LE;

      struct sqlite3_index_constraint *pCons = &pIdxInfo->aConstraint[i];
      if( pCons->usable 
       && pCons->iColumn>=0 
       && p->pTab->aCol[pCons->iColumn].iPk==0
       && (pCons->op & opmask) 
      ){
        IdxConstraint *pNew;
        const char *zColl = sqlite3_vtab_collation(pIdxInfo, i);
        pNew = idxNewConstraint(&rc, zColl);
        if( pNew ){
          pNew->iCol = pCons->iColumn;
          if( pCons->op==SQLITE_INDEX_CONSTRAINT_EQ ){
            pNew->pNext = pScan->pEq;
            pScan->pEq = pNew;
          }else{

/*
** CAPI3REF: Determine The Collation For a Virtual Table Constraint
**
** This function may only be called from within a call to the [xBestIndex]
** method of a [virtual table implementation]. 
**
** The first argument must be the sqlite3_index_info object that is the

** first parameter to the xBestIndex() method. The second argument must be
** an index into the aConstraint[] array belonging to the sqlite3_index_info
** structure passed to xBestIndex. This function returns a pointer to a buffer 
** containing the name of the collation sequence for the corresponding
** constraint.
*/
SQLITE_EXPERIMENTAL const char *sqlite3_vtab_collation(sqlite3_index_info*,int);

/*
** CAPI3REF: Conflict resolution modes
** KEYWORDS: {conflict resolution mode}
**
** These constants are returned by [sqlite3_vtab_on_conflict()] to
** inform a [virtual table] implementation what the [ON CONFLICT] mode

  unsigned nProgressOps;        /* Number of opcodes for progress callback */
#endif
#ifndef SQLITE_OMIT_VIRTUALTABLE
  int nVTrans;                  /* Allocated size of aVTrans */
  Hash aModule;                 /* populated by sqlite3_create_module() */
  VtabCtx *pVtabCtx;            /* Context for active vtab connect/create */
  VTable **aVTrans;             /* Virtual tables with open transactions */
  VTable *pDisconnect;          /* Disconnect these in next sqlite3_prepare() */

#endif
  Hash aFunc;                   /* Hash table of connection functions */
  Hash aCollSeq;                /* All collating sequences */
  BusyHandler busyHandler;      /* Busy callback */
  Db aDbStatic[2];              /* Static space for the 2 default backends */
  Savepoint *pSavepoint;        /* List of active savepoints */
  int busyTimeout;              /* Busy handler timeout, in msec */

** generating the code that loops through a table looking for applicable
** rows.  Indices are selected and used to speed the search when doing
** so is applicable.  Because this module is responsible for selecting
** indices, you might also think of this module as the "query optimizer".
*/
#include "sqliteInt.h"
#include "whereInt.h"

/*
** Extra information appended to the end of sqlite3_index_info but not
** visible to the xBestIndex function, at least not directly.  The
** sqlite3_vtab_collation() interface knows how to reach it, however.
**
** This object is not an API and can be changed from one release to the
** next.  As long as allocateIndexInfo() and sqlite3_vtab_collation()
** agree on the structure, all will be well.
*/
typedef struct HiddenIndexInfo HiddenIndexInfo;
struct HiddenIndexInfo {
  WhereClause *pWC;   /* The Where clause being analyzed */
  Parse *pParse;      /* The parsing context */
};

/* Forward declaration of methods */
static int whereLoopResize(sqlite3*, WhereLoop*, int);

/* Test variable that can be set to enable WHERE tracing */
#if defined(SQLITE_TEST) || defined(SQLITE_DEBUG)
/***/ int sqlite3WhereTrace = 0;

#ifndef SQLITE_OMIT_VIRTUALTABLE
/*
** Allocate and populate an sqlite3_index_info structure. It is the 
** responsibility of the caller to eventually release the structure
** by passing the pointer returned by this function to sqlite3_free().
*/
static sqlite3_index_info *allocateIndexInfo(
  Parse *pParse,                  /* The parsing context */
  WhereClause *pWC,               /* The WHERE clause being analyzed */
  Bitmask mUnusable,              /* Ignore terms with these prereqs */
  struct SrcList_item *pSrc,      /* The FROM clause term that is the vtab */
  ExprList *pOrderBy,             /* The ORDER BY clause */
  u16 *pmNoOmit                   /* Mask of terms not to omit */
){
  int i, j;
  int nTerm;
  struct sqlite3_index_constraint *pIdxCons;
  struct sqlite3_index_orderby *pIdxOrderBy;
  struct sqlite3_index_constraint_usage *pUsage;
  struct HiddenIndexInfo *pHidden;
  WhereTerm *pTerm;
  int nOrderBy;
  sqlite3_index_info *pIdxInfo;
  u16 mNoOmit = 0;

  /* Count the number of possible WHERE clause constraints referring
  ** to this virtual table */

    }
  }

  /* Allocate the sqlite3_index_info structure
  */
  pIdxInfo = sqlite3DbMallocZero(pParse->db, sizeof(*pIdxInfo)
                           + (sizeof(*pIdxCons) + sizeof(*pUsage))*nTerm
                           + sizeof(*pIdxOrderBy)*nOrderBy + sizeof(*pHidden) );
  if( pIdxInfo==0 ){
    sqlite3ErrorMsg(pParse, "out of memory");
    return 0;
  }

  /* Initialize the structure.  The sqlite3_index_info structure contains
  ** many fields that are declared "const" to prevent xBestIndex from
  ** changing them.  We have to do some funky casting in order to
  ** initialize those fields.
  */
  pHidden = (struct HiddenIndexInfo*)&pIdxInfo[1];
  pIdxCons = (struct sqlite3_index_constraint*)&pHidden[1];
  pIdxOrderBy = (struct sqlite3_index_orderby*)&pIdxCons[nTerm];
  pUsage = (struct sqlite3_index_constraint_usage*)&pIdxOrderBy[nOrderBy];
  *(int*)&pIdxInfo->nConstraint = nTerm;
  *(int*)&pIdxInfo->nOrderBy = nOrderBy;
  *(struct sqlite3_index_constraint**)&pIdxInfo->aConstraint = pIdxCons;
  *(struct sqlite3_index_orderby**)&pIdxInfo->aOrderBy = pIdxOrderBy;
  *(struct sqlite3_index_constraint_usage**)&pIdxInfo->aConstraintUsage =
                                                                   pUsage;

  pHidden->pWC = pWC;
  pHidden->pParse = pParse;
  for(i=j=0, pTerm=pWC->a; i<pWC->nTerm; i++, pTerm++){
    u16 op;
    if( pTerm->leftCursor != pSrc->iCursor ) continue;
    if( pTerm->prereqRight & mUnusable ) continue;
    assert( IsPowerOfTwo(pTerm->eOperator & ~WO_EQUIV) );
    testcase( pTerm->eOperator & WO_IN );
    testcase( pTerm->eOperator & WO_IS );

  WHERETRACE(0xffff, ("  bIn=%d prereqIn=%04llx prereqOut=%04llx\n",
                      *pbIn, (sqlite3_uint64)mPrereq,
                      (sqlite3_uint64)(pNew->prereq & ~mPrereq)));

  return rc;
}












/*
** If this function is invoked from within an xBestIndex() callback, it
** returns a pointer to a buffer containing the name of the collation
** sequence associated with element iCons of the sqlite3_index_info.aConstraint
** array. Or, if iCons is out of range or there is no active xBestIndex
** call, return NULL.
*/
const char *sqlite3_vtab_collation(sqlite3_index_info *pIdxInfo, int iCons){
  HiddenIndexInfo *pHidden = (HiddenIndexInfo*)&pIdxInfo[1];
  const char *zRet = 0;
  if( iCons>=0 && iCons<pIdxInfo->nConstraint ){
    CollSeq *pC = 0;
    int iTerm = pIdxInfo->aConstraint[iCons].iTermOffset;
    Expr *pX = pHidden->pWC->a[iTerm].pExpr;
    if( pX->pLeft ){
      pC = sqlite3BinaryCompareCollSeq(pHidden->pParse, pX->pLeft, pX->pRight);
    }
    zRet = (pC ? pC->zName : "BINARY");
  }
  return zRet;
}

/*

  struct SrcList_item *pSrc;   /* The FROM clause term to search */
  sqlite3_index_info *p;       /* Object to pass to xBestIndex() */
  int nConstraint;             /* Number of constraints in p */
  int bIn;                     /* True if plan uses IN(...) operator */
  WhereLoop *pNew;
  Bitmask mBest;               /* Tables used by best possible plan */
  u16 mNoOmit;



  assert( (mPrereq & mUnusable)==0 );
  pWInfo = pBuilder->pWInfo;
  pParse = pWInfo->pParse;
  pWC = pBuilder->pWC;
  pNew = pBuilder->pNew;
  pSrc = &pWInfo->pTabList->a[pNew->iTab];

  pNew->u.vtab.needFree = 0;
  nConstraint = p->nConstraint;
  if( whereLoopResize(pParse->db, pNew, nConstraint) ){
    sqlite3DbFree(pParse->db, p);
    return SQLITE_NOMEM_BKPT;
  }







  /* First call xBestIndex() with all constraints usable. */
  WHERETRACE(0x40, ("  VirtualOne: all usable\n"));
  rc = whereLoopAddVirtualOne(pBuilder, mPrereq, ALLBITS, 0, p, mNoOmit, &bIn);

  /* If the call to xBestIndex() with all terms enabled produced a plan
  ** that does not require any source tables (IOW: a plan with mBest==0),
  ** then there is no point in making any further calls to xBestIndex() 

      rc = whereLoopAddVirtualOne(
          pBuilder, mPrereq, mPrereq, WO_IN, p, mNoOmit, &bIn);
    }
  }

  if( p->needToFreeIdxStr ) sqlite3_free(p->idxStr);
  sqlite3DbFreeNN(pParse->db, p);

  return rc;
}
#endif /* SQLITE_OMIT_VIRTUALTABLE */

/*
** Add WhereLoop entries to handle OR terms.  This works for either
** btrees or virtual tables.