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Implement DESCRIBE SELECT to show schema rather than EXPLAIN plan #18238

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Merged
alamb merged 5 commits into from
Oct 26, 2025
Merged

Implement DESCRIBE SELECT to show schema rather than EXPLAIN plan #18238

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f394643
feat: Implement DESCRIBE SELECT
djanderson Oct 23, 2025
76a9dc6
test: Add slt tests for describing statements
djanderson Oct 25, 2025
bb09487
docs: Describe change in upgrade guide
djanderson Oct 26, 2025
e2715f6
style: Match prettier's expected formatting
djanderson Oct 26, 2025
c95e564
refactor: Use not_impl_err macro
djanderson Oct 26, 2025
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23 changes: 23 additions & 0 deletions datafusion/sql/src/statement.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -242,6 +242,16 @@ impl<S: ContextProvider> SqlToRel<'_, S> {
table_name,
..
} => self.describe_table_to_plan(table_name),
Statement::Explain {
describe_alias: DescribeAlias::Describe | DescribeAlias::Desc, // only parse 'DESCRIBE statement' or 'DESC statement' and not 'EXPLAIN statement'
statement,
..
} => match *statement {
Statement::Query(query) => self.describe_query_to_plan(*query),
_ => Err(DataFusionError::NotImplemented(format!(
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"Unsupported statement type for DESCRIBE: {statement:?}",
))),
},
Statement::Explain {
verbose,
statement,
Expand Down Expand Up @@ -1396,6 +1406,19 @@ impl<S: ContextProvider> SqlToRel<'_, S> {
}))
}

fn describe_query_to_plan(&self, query: Query) -> Result<LogicalPlan> {
let plan = self.query_to_plan(query, &mut PlannerContext::new())?;

let schema = Arc::new(plan.schema().as_arrow().clone());

let output_schema = DFSchema::try_from(LogicalPlan::describe_schema()).unwrap();

Ok(LogicalPlan::DescribeTable(DescribeTable {
schema,
output_schema: Arc::new(output_schema),
}))
}

fn copy_to_plan(&self, statement: CopyToStatement) -> Result<LogicalPlan> {
// Determine if source is table or query and handle accordingly
let copy_source = statement.source;
Expand Down