explain with cte1 as materialized (
    select a, count(*) as cnt
    from t 
    group by a
)
select * from cte1 as c1 where c1.a = 1
union all
select * from cte1 as c2 where c2.a = 2;
----
Sequence
├── MaterializedCTE: cte1
│   └── AggregateFinal
│       ├── output columns: [COUNT(*) (#3), t.a (#0)]
│       ├── group by: [a]
│       ├── aggregate functions: [count()]
│       ├── estimated rows: 2.00
│       └── AggregatePartial
│           ├── group by: [a]
│           ├── aggregate functions: [count()]
│           ├── estimated rows: 2.00
│           └── Filter
│               ├── output columns: [t.a (#0)]
│               ├── filters: [is_true((t.a (#0) = 1 OR t.a (#0) = 2))]
│               ├── estimated rows: 2.78
│               └── TableScan
│                   ├── table: default.default.t
│                   ├── output columns: [a (#0)]
│                   ├── read rows: 5
│                   ├── read size: < 1 KiB
│                   ├── partitions total: 1
│                   ├── partitions scanned: 1
│                   ├── pruning stats: [segments: <range pruning: 1 to 1>, blocks: <range pruning: 1 to 1, bloom pruning: 1 to 1>]
│                   ├── push downs: [filters: [is_true((t.a (#0) = 1 OR t.a (#0) = 2))], limit: NONE]
│                   └── estimated rows: 5.00
└── UnionAll
    ├── output columns: [a (#12), cnt (#13)]
    ├── estimated rows: 2.00
    ├── Filter
    │   ├── output columns: [t.a (#4), COUNT(*) (#7)]
    │   ├── filters: [is_true(c1.a (#4) = 1)]
    │   ├── estimated rows: 1.00
    │   └── MaterializeCTERef
    │       ├── cte_name: cte1
    │       ├── cte_schema: [a (#4), COUNT(*) (#7)]
    │       └── estimated rows: 3.00
    └── Filter
        ├── output columns: [t.a (#8), COUNT(*) (#11)]
        ├── filters: [is_true(c2.a (#8) = 2)]
        ├── estimated rows: 1.00
        └── MaterializeCTERef
            ├── cte_name: cte1
            ├── cte_schema: [a (#8), COUNT(*) (#11)]
            └── estimated rows: 3.00