## What changes were proposed in this pull request?
Two new rules in the logical plan optimizers are added.
1. When there is only one element in the **`Collection`**, the
physical plan will be optimized to **`EqualTo`**, so predicate
pushdown can be used.
```scala
profileDF.filter( $"profileID".isInCollection(Set(6))).explain(true)
"""
|== Physical Plan ==
|*(1) Project [profileID#0]
|+- *(1) Filter (isnotnull(profileID#0) && (profileID#0 = 6))
| +- *(1) FileScan parquet [profileID#0] Batched: true, Format: Parquet,
| PartitionFilters: [],
| PushedFilters: [IsNotNull(profileID), EqualTo(profileID,6)],
| ReadSchema: struct<profileID:int>
""".stripMargin
```
2. When the **`Collection`** is empty, and the input is nullable, the
logical plan will be simplified to
```scala
profileDF.filter( $"profileID".isInCollection(Set())).explain(true)
"""
|== Optimized Logical Plan ==
|Filter if (isnull(profileID#0)) null else false
|+- Relation[profileID#0] parquet
""".stripMargin
```
TODO:
1. For multiple conditions with numbers less than certain thresholds,
we should still allow predicate pushdown.
2. Optimize the **`In`** using **`tableswitch`** or **`lookupswitch`**
when the numbers of the categories are low, and they are **`Int`**,
**`Long`**.
3. The default immutable hash trees set is slow for query, and we
should do benchmark for using different set implementation for faster
query.
4. **`filter(if (condition) null else false)`** can be optimized to false.
## How was this patch tested?
Couple new tests are added.
Author: DB Tsai <d_tsai@apple.com>
Closes#21442 from dbtsai/optimize-in.
0f0d1865f5