**   (?,?,?) IN (SELECT a, b, c FROM t1)
**   CREATE INDEX i1 ON t1(b, c, a);
**
** then aiMap[] is populated with {2, 0, 1}.
*/
#ifndef SQLITE_OMIT_SUBQUERY
int sqlite3FindInIndex(
  Parse *pParse, 
  Expr *pX, 
  u32 inFlags, 
  int *prRhsHasNull,
  int *aiMap
){
  Select *p;                            /* SELECT to the right of IN operator */
  int eType = 0;                        /* Type of RHS table. IN_INDEX_* */
  int iTab = pParse->nTab++;            /* Cursor of the RHS table */
  int mustBeUnique;                     /* True if RHS must be unique */
  Vdbe *v = sqlite3GetVdbe(pParse);     /* Virtual machine being coded */

................................................................................
      }

      /* The collation sequence used by the comparison. If an index is to
      ** be used in place of a temp-table, it must be ordered according
      ** to this collation sequence.  */

      for(pIdx=pTab->pIndex; pIdx && eType==0 && affinity_ok; pIdx=pIdx->pNext){


        if( pIdx->nKeyCol<nExpr ) continue;
        if( mustBeUnique && (pIdx->nKeyCol!=nExpr || !IsUniqueIndex(pIdx)) ){

          continue;

        }

        for(i=0; i<nExpr; i++){
          Expr *pLhs = sqlite3VectorFieldSubexpr(pX->pLeft, i);
          Expr *pRhs = pEList->a[i].pExpr;
          CollSeq *pReq = sqlite3BinaryCompareCollSeq(pParse, pLhs, pRhs);
          int j;

          if( pReq==0 ) break;

          for(j=0; j<nExpr; j++){
            if( pIdx->aiColumn[j]!=pRhs->iColumn ) continue;
            assert( pIdx->azColl[j] );

            if( sqlite3StrICmp(pReq->zName, pIdx->azColl[j])!=0 ) continue;
            break;
          }
          if( j==nExpr ) break;
          if( aiMap ) aiMap[i] = j;
        }

**   (?,?,?) IN (SELECT a, b, c FROM t1)
**   CREATE INDEX i1 ON t1(b, c, a);
**
** then aiMap[] is populated with {2, 0, 1}.
*/
#ifndef SQLITE_OMIT_SUBQUERY
int sqlite3FindInIndex(
  Parse *pParse,             /* Parsing context */
  Expr *pX,                  /* The right-hand side (RHS) of the IN operator */
  u32 inFlags,               /* IN_INDEX_LOOP, _MEMBERSHIP, and/or _NOOP_OK */
  int *prRhsHasNull,         /* Register holding NULL status.  See notes */
  int *aiMap                 /* Mapping from Index fields to RHS fields */
){
  Select *p;                            /* SELECT to the right of IN operator */
  int eType = 0;                        /* Type of RHS table. IN_INDEX_* */
  int iTab = pParse->nTab++;            /* Cursor of the RHS table */
  int mustBeUnique;                     /* True if RHS must be unique */
  Vdbe *v = sqlite3GetVdbe(pParse);     /* Virtual machine being coded */

................................................................................
      }

      /* The collation sequence used by the comparison. If an index is to
      ** be used in place of a temp-table, it must be ordered according
      ** to this collation sequence.  */

      for(pIdx=pTab->pIndex; pIdx && eType==0 && affinity_ok; pIdx=pIdx->pNext){
        if( pIdx->nColumn<nExpr ) continue;
        if( mustBeUnique ){
          if( pIdx->nKeyCol>nExpr
           ||(pIdx->nColumn>nExpr && !IsUniqueIndex(pIdx))
          ){
            continue;
          }
        }

        for(i=0; i<nExpr; i++){
          Expr *pLhs = sqlite3VectorFieldSubexpr(pX->pLeft, i);
          Expr *pRhs = pEList->a[i].pExpr;
          CollSeq *pReq = sqlite3BinaryCompareCollSeq(pParse, pLhs, pRhs);
          int j;

          assert( pReq!=0 || pRhs->iColumn==XN_ROWID || pParse->nErr );

          for(j=0; j<nExpr; j++){
            if( pIdx->aiColumn[j]!=pRhs->iColumn ) continue;
            assert( pIdx->azColl[j] );
            if( pReq==0 ) continue;
            if( sqlite3StrICmp(pReq->zName, pIdx->azColl[j])!=0 ) continue;
            break;
          }
          if( j==nExpr ) break;
          if( aiMap ) aiMap[i] = j;
        }