# JoinFilter
```rust
pub struct JoinFilter {
/// Filter expression，列引用的输入 schema 是 JoinFilter 的 schema 字段
expression: Arc<dyn PhysicalExpr>,
/// Column indices required to construct intermediate batch for filtering
column_indices: Vec<ColumnIndex>,
/// Physical schema of intermediate batch
/// 这个 schema 跟 column_indices 保持一致的，生成中间 batch 用于计算 expression
schema: Schema,
}
```
```rust
pub struct ColumnIndex {
/// Index of the column，在左边/右边输出的 index
pub index: usize,
/// Whether the column is at the left or right side
pub side: JoinSide,
}
```