This question is based on my [Non-covering indexes and trivial optimization](https://topanswers.xyz/databases?q=1362) post. While writing it, I have made an observation regarding full optimization case that raised the question.

So, these were the rules applied during plan search

```none
---------------------------------------------------
Apply Rule: SelectToFilter - Select()->Filter()
---------------------------------------------------
Apply Rule: GetToScan - Get()->Scan()
---------------------------------------------------
Apply Rule: GetToIdxScan - Get -> IdxScan
```

The final physical plan is via `SelectToFilter` and `GetToIdxScan`.

Difference of snapshots of information returned by `sys.dm_exec_query_transformation_stats` before and after query compilation shows that all rules succeeded

| name | built_substitute | succeeded |
| ---- | ----------------:| ---------:|
| GetToIdxScan | 1 | 1 |
| GetToScan | 1 | 1 |
| SelectToFilter | 1 | 1 |

Following is what `GetToScan` rule generated

```none
---------------------------------------------------
Apply Rule: GetToScan - Get()->Scan()
    Args: Grp 3 0 LogOp_Get (Distance = 0)

Rule Result: group=3 1 <GetToScan>PhyOp_TableScan (Distance = 1)

Subst:
  PhyOp_TableScan TBL: #Data Bmk ( K) IsRow: COL: IsBaseRow1000 
```

The result of this rule (`group=3 1`) is not in the Final Memo Structure however

```none
--- Final Memo Structure ---
Root Group 4: Card=1 (Max=10000, Min=0)
   1 <SelectToFilter>PhyOp_Filter 3.2 2.0  Cost(RowGoal 0,ReW 0,ReB 0,Dist 0,Total 0)= 0.00782654 (Distance = 1)
   0 LogOp_Select 3 2 (Distance = 0)
Group 3: Card=1001 (Max=10000, Min=0)
   2 <GetToIdxScan>PhyOp_Range 1 ASC   Cost(RowGoal 0,ReW 0,ReB 0,Dist 0,Total 0)= 0.00734606 (Distance = 1)
   0 LogOp_Get (Distance = 0)
Group 2: 
   0 ScaOp_Comp  0.0 1.0  Cost(RowGoal 0,ReW 0,ReB 0,Dist 0,Total 0)= 3 (Distance = 0)
Group 1: 
   0 ScaOp_Const   Cost(RowGoal 0,ReW 0,ReB 0,Dist 0,Total 0)= 1 (Distance = 0)
Group 0: 
   0 ScaOp_Identifier   Cost(RowGoal 0,ReW 0,ReB 0,Dist 0,Total 0)= 1 (Distance = 0)
----------------------------
```

which means that this alternative was discarded.

Why was `PhyOp_TableScan` alternative discarded, and why does it not with `QUERYRULEOFF GetToIdxScan`? Why can alternatives be discarded in general, what is the mechanism?