SQLite

    pNew->u.btree.nEq++;
    pNew->u.btree.nSkip++;
    pNew->aLTerm[pNew->nLTerm++] = 0;
    pNew->wsFlags |= WHERE_SKIPSCAN;
    nIter = pProbe->aiRowLogEst[saved_nEq] - pProbe->aiRowLogEst[saved_nEq+1];
    if( pTerm ){
      /* TUNING:  When estimating skip-scan for a term that is also indexable,
      ** multiply the cost of the skip-scan by 2.0, to make it a little less
      ** desirable than the regular index lookup. */
      nIter += 10;  assert( 10==sqlite3LogEst(2) );
    }
    pNew->nOut -= nIter;
    /* TUNING:  Because uncertainties in the estimates for skip-scan queries,
    ** add a 1.375 fudge factor to make skip-scan slightly less likely. */
    nIter += 5;
    whereLoopAddBtreeIndex(pBuilder, pSrc, pProbe, nIter + nInMul);
    pNew->nOut = saved_nOut;
    pNew->u.btree.nEq = saved_nEq;
    pNew->u.btree.nSkip = saved_nSkip;
  }
  for(; rc==SQLITE_OK && pTerm!=0; pTerm = whereScanNext(&scan)){
    u16 eOp = pTerm->eOperator;   /* Shorthand for pTerm->eOperator */

} {}
db cache flush
do_execsql_test skipscan1-5.3 {
  EXPLAIN QUERY PLAN
    SELECT xh, loc FROM t5 WHERE loc >= 'M' AND loc < 'N';
} {/.*COVERING INDEX t5i1 .*/}

# The column used by the skip-scan needs to be sufficiently selective.
# See the private email from Adi Zaimi to drh@sqlite.org on 2014-09-22.
#
db close
forcedelete test.db
sqlite3 db test.db
do_execsql_test skipscan1-6.1 {
  CREATE TABLE t1(a,b,c,d,e,f,g,h varchar(300));
  CREATE INDEX t1ab ON t1(a,b);
  ANALYZE sqlite_master;
  -- Only two distinct values for the skip-scan column.  Skip-scan is not used.
  INSERT INTO sqlite_stat1 VALUES('t1','t1ab','500000 250000 125000');
  ANALYZE sqlite_master;
  EXPLAIN QUERY PLAN SELECT * FROM t1 WHERE b=1;
} {~/ANY/}
do_execsql_test skipscan1-6.2 {
  -- Four distinct values for the skip-scan column.  Skip-scan is used.
  UPDATE sqlite_stat1 SET stat='500000 250000 62500';
  ANALYZE sqlite_master;
  EXPLAIN QUERY PLAN SELECT * FROM t1 WHERE b=1;
} {/ANY.a. AND b=/}
do_execsql_test skipscan1-6.3 {
  -- Two distinct values for the skip-scan column again.  Skip-scan is not used.
  UPDATE sqlite_stat1 SET stat='500000 125000 62500';
  ANALYZE sqlite_master;
  EXPLAIN QUERY PLAN SELECT * FROM t1 WHERE b=1;
} {~/ANY/}

finish_test

  foreach {tn2 q res} {
    1 { c BETWEEN 'd' AND 'e' }       {/*ANY(a) AND ANY(b) AND c>? AND c<?*/}
    2 { c BETWEEN 'b' AND 'r' }       {/*SCAN TABLE t2*/}
    3 { c > 'q' }                     {/*ANY(a) AND ANY(b) AND c>?*/}
    4 { c > 'e' }                     {/*SCAN TABLE t2*/}
    5 { c < 'q' }                     {/*SCAN TABLE t2*/}
    6 { c < 'c' }                     {/*ANY(a) AND ANY(b) AND c<?*/}
  } {
    set sql "EXPLAIN QUERY PLAN SELECT * FROM t2 WHERE $q" 
    do_execsql_test 2.$tn.$tn2 $sql $res
  }

}

  6 "b < 'zzz'"                        {/*SCAN TABLE t3*/}
} {
  set sql "EXPLAIN QUERY PLAN SELECT * FROM t3 WHERE $q" 
  do_execsql_test 3.3.$tn $sql $res
}

finish_test