alamb commented on code in PR #8132:
URL: https://github.com/apache/arrow-datafusion/pull/8132#discussion_r1390389405
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datafusion/common/src/dfschema.rs:
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@@ -34,10 +34,75 @@ use crate::{
use arrow::compute::can_cast_types;
use arrow::datatypes::{DataType, Field, FieldRef, Fields, Schema, SchemaRef};
-/// A reference-counted reference to a `DFSchema`.
+/// A reference-counted reference to a [DFSchema].
pub type DFSchemaRef = Arc<DFSchema>;
-/// DFSchema wraps an Arrow schema and adds relation names
+/// DFSchema wraps an Arrow schema and adds relation names.
+///
+/// The schema may hold the fields across multiple tables. Some fields may be
+/// qualified and some unqualified. A qualified field is a field that has a
+/// relation name associated with it.
+///
+/// Unqualified fields must be unique not only amongst themselves, but also
must
+/// have a distinct name from any qualified field names. This allows finding a
+/// qualified field by name to be possible, so long as there aren't multiple
+/// qualified fields with the same name.
+///
+/// There is an alias to `Arc<DFSchema>` named [DFSchemaRef].
+///
+/// # Creating qualified schemas
+///
+/// Use [DFSchema::try_from_qualified_schema] to create a qualified schema from
+/// an Arrow schema.
+///
+/// ```rust
+/// use datafusion_common::{DFSchema, Column};
+/// use arrow_schema::{DataType, Field, Schema};
+///
+/// let arrow_schema = Schema::new(vec![
+/// Field::new("c1", DataType::Int32, false),
+/// ]);
+///
+/// let df_schema = DFSchema::try_from_qualified_schema("t1",
&arrow_schema).unwrap();
+/// let column = Column::from_qualified_name("t1.c1");
+/// assert!(df_schema.has_column(&column));
+///
+/// // Can also access qualified fields with unqualified name, if it's
unambiguous
+/// let column = Column::from_qualified_name("c1");
+/// assert!(df_schema.has_column(&column));
+/// ```
+///
+/// # Creating unqualified schemas
+///
+/// Create an unqualified schema using TryFrom:
+///
+/// ```rust
+/// use datafusion_common::{DFSchema, Column};
+/// use arrow_schema::{DataType, Field, Schema};
+///
+/// let arrow_schema = Schema::new(vec![
+/// Field::new("c1", DataType::Int32, false),
+/// ]);
+///
+/// let df_schema = DFSchema::try_from(arrow_schema).unwrap();
+/// let column = Column::new_unqualified("c1");
+/// assert!(df_schema.has_column(&column));
+/// ```
+///
+/// # Converting back to Arrow schema
Review Comment:
Thank you @wjones127 this is super helpful
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