SQLite

        || (pNew->wsFlags & WHERE_COLUMN_NULL)!=0 
        || (pNew->wsFlags & WHERE_COLUMN_IN)!=0 
        || (pNew->wsFlags & WHERE_SKIPSCAN)!=0 
    );

    if( eOp & WO_IN ){
      Expr *pExpr = pTerm->pExpr;
      LogEst M, logK;
      if( ExprHasProperty(pExpr, EP_xIsSelect) ){
        /* "x IN (SELECT ...)":  TUNING: the SELECT returns 25 rows */
        int i;
        nIn = 46;  assert( 46==sqlite3LogEst(25) );

        /* The expression may actually be of the form (x, y) IN (SELECT...).
        ** In this case there is a separate term for each of (x) and (y).
        ** However, the nIn multiplier should only be applied once, not once
        ** for each such term. The following loop checks that pTerm is the
        ** first such term in use, and sets nIn back to 0 if it is not. */
        for(i=0; i<pNew->nLTerm-1; i++){
          if( pNew->aLTerm[i] && pNew->aLTerm[i]->pExpr==pExpr ) nIn = 0;
        }
      }else if( ALWAYS(pExpr->x.pList && pExpr->x.pList->nExpr) ){
        /* "x IN (value, value, ...)" */
        nIn = sqlite3LogEst(pExpr->x.pList->nExpr);
        assert( nIn>0 );  /* RHS always has 2 or more terms...  The parser
                          ** changes "x IN (?)" into "x=?". */
      }
      if( pProbe->hasStat1 ){
        /* Let:
        **   N = the total number of rows in the table
        **   K = the number of entries on the RHS of the IN operator
        **   M = the number of rows in the table that match terms to the 
        **       to the left in the same index.  If the IN operator is on
        **       the left-most index column, M==N.
        **
        ** Given the definitions above, it is better to omit the IN operator
        ** from the index lookup and instead do a scan of the M elements,
        ** testing each scanned row against the IN operator separately, if:
        **
        **        M*log(K) < K*log(N)
        **
        ** Our estimates for M, K, and N might be inaccurate, so we build in
        ** a safety margin of 2 (LogEst: 10) that favors using the IN operator
        ** with the index, as using an index has better worst-case behavior.
        ** If we do not have real sqlite_stat1 data, always prefer to use
        ** the index.
        */
        M = pProbe->aiRowLogEst[saved_nEq];
        logK = estLog(nIn);
        if( M + logK + 10 < nIn + rLogSize ){
          WHERETRACE(0x40,
            ("Scan preferred over IN operator on column %d of \"%s\" (%d<%d)\n",
             saved_nEq, pProbe->zName, M+logK+10, nIn+rLogSize));
          continue;
        }else{
          WHERETRACE(0x40,
            ("IN operator preferred on column %d of \"%s\" (%d>=%d)\n",
             saved_nEq, pProbe->zName, M+logK+10, nIn+rLogSize));
        }
      }
      pNew->wsFlags |= WHERE_COLUMN_IN;
    }else if( eOp & (WO_EQ|WO_IS) ){
      int iCol = pProbe->aiColumn[saved_nEq];
      pNew->wsFlags |= WHERE_COLUMN_EQ;
      assert( saved_nEq==pNew->u.btree.nEq );
      if( iCol==XN_ROWID 
       || (iCol>=0 && nInMul==0 && saved_nEq==pProbe->nKeyCol-1)
      ){

do_test in6-1.1 {
  db eval {
    CREATE TABLE t1(a,b,c,d);
    WITH RECURSIVE c(x) AS (VALUES(1) UNION ALL SELECT x+1 FROM c WHERE x<100)
      INSERT INTO t1(a,b,c,d)
        SELECT 100, 200+x/2, 300+x/5, x FROM c;
    CREATE INDEX t1abc ON t1(a,b,c);
    ANALYZE;
    UPDATE sqlite_stat1 SET stat='1000000 500000 500 50';
    ANALYZE sqlite_master;
  }
  set ::sqlite_search_count 0
  db eval {
    SELECT d FROM t1
     WHERE a=99
       AND b IN (200,205,201,204)
       AND c IN (304,302,309,308);

  CREATE TABLE d2(a, b, c);
  CREATE INDEX d2ab ON d2(a, b);
  CREATE INDEX d2c ON d2(c);

  WITH i(i) AS (
    VALUES(1) UNION ALL SELECT i+1 FROM i WHERE i<1000
  )
  INSERT INTO d2 SELECT i/100, i%100, i/100 FROM i;
  ANALYZE;
}

do_eqp_test 5.1 {
  SELECT * FROM d2 WHERE 
    (a, b) IN (SELECT x, y FROM d1) AND
    (c) IN (SELECT y FROM d1)