Function cast_subquery

datafusion/expr/src/expr_schema.rs:762–792

Cast subquery in InSubquery/ScalarSubquery to a given type. 1. **Projection plan**: If the subquery is a projection (i.e. a SELECT statement with specific columns), it casts the first expression in the projection to the target type and creates a new projection with the casted expression. 2. **Non-projection plan**: If the subquery isn't a projection, it adds a projection to the plan with the cast

(subquery: Subquery, cast_to_type: &DataType)

/// 2. **Non-projection plan**: If the subquery isn't a projection, it adds a projection to the plan
///    with the casted first column.
pub fn cast_subquery(subquery: Subquery, cast_to_type: &DataType) -> Result<Subquery> {
    if subquery.subquery.schema().field(0).data_type() == cast_to_type {
        return Ok(subquery);
    }

    let plan = subquery.subquery.as_ref();
    let new_plan = match plan {
        LogicalPlan::Projection(projection) => {
            let cast_expr = projection.expr[0]
                .clone()
                .cast_to(cast_to_type, projection.input.schema())?;
            LogicalPlan::Projection(Projection::try_new(
                vec![cast_expr],
                Arc::clone(&projection.input),
            )?)
        }
        _ => {
            let cast_expr = Expr::Column(Column::from(plan.schema().qualified_field(0)))
                .cast_to(cast_to_type, subquery.subquery.schema())?;
            LogicalPlan::Projection(Projection::try_new(
                vec![cast_expr],
                subquery.subquery,
            )?)
        }
    };
    Ok(Subquery {
        subquery: Arc::new(new_plan),
        outer_ref_columns: subquery.outer_ref_columns,
        spans: Spans::new(),
    })
}

#[cfg(test)]
mod tests {