SQLite

  }
}

/*
** Return TRUE if all of the following are true:
**
**   (1)  X has the same or lower cost that Y
**   (2)  X is a proper subset of Y
**   (3)  X skips at least as many columns as Y
**   (2)  X users fewer WHERE clause terms than Y
**   (3)  Every WHERE clause term used by X is also used by Y
**   (4)  X skips at least as many columns as Y
**   (5)  If X is a covering index, than Y is too
**
** By "proper subset" we mean that X uses fewer WHERE clause terms
** Conditions (2) and (3) mean that X is a "proper subset" of Y.
** than Y and that every WHERE clause term used by X is also used
** by Y.
**
** If X is a proper subset of Y then Y is a better choice and ought
** to have a lower cost.  This routine returns TRUE when that cost 
** relationship is inverted and needs to be adjusted.  The third rule
** relationship is inverted and needs to be adjusted.  Constraint (4)
** was added because if X uses skip-scan less than Y it still might
** deserve a lower cost even if it is a proper subset of Y.
*/
static int whereLoopCheaperProperSubset(
  const WhereLoop *pX,       /* First WhereLoop to compare */
  const WhereLoop *pY        /* Compare against this WhereLoop */
){

  }
  for(i=pX->nLTerm-1; i>=0; i--){
    if( pX->aLTerm[i]==0 ) continue;
    for(j=pY->nLTerm-1; j>=0; j--){
      if( pY->aLTerm[j]==pX->aLTerm[i] ) break;
    }
    if( j<0 ) return 0;  /* X not a subset of Y since term X[i] not used by Y */
  }
  if( (pX->wsFlags&WHERE_IDX_ONLY)!=0 
   && (pY->wsFlags&WHERE_IDX_ONLY)==0 ){
    return 0;  /* Constraint (5) */
  }
  return 1;  /* All conditions meet */
}

/*
** Try to adjust the cost of WhereLoop pTemplate upwards or downwards so
** that:

  INSERT INTO t4 SELECT a, b, c, d, e, f FROM data;
  ANALYZE;
} {}

do_eqp_test 23.1 {
  SELECT * FROM t4 WHERE 
    (e=1 AND b='xyz' AND c='zyx' AND a<'AEA') AND f<300
  -- Formerly used index i41.  But i41 is not a covering index whereas
  -- the PRIMARY KEY is a covering index, and so as of 2017-10-15, the
  -- PRIMARY KEY is preferred.
} {
  0 0 0 {SEARCH TABLE t4 USING INDEX i41 (e=? AND c=? AND b=? AND a<?)}
  0 0 0 {SEARCH TABLE t4 USING PRIMARY KEY (c=? AND b=? AND a<?)}
}
do_eqp_test 23.2 {
  SELECT * FROM t4 WHERE 
    (e=1 AND b='xyz' AND c='zyx' AND a<'JJJ') AND f<300
} {
  0 0 0 {SEARCH TABLE t4 USING INDEX i42 (f<?)}
}