[Feature] support describe file (#4995)

To know the columns/types in a file, users has to create an external table, and describe the table.
Sometimes the infer schema is wrong for creating table, to make it right, user need to drop the table, and recreate a table with the specify schema.
To solve this problem, we add describe file interface in datafusion-clie, With the Describe File, user can know the infer schema is wrong before creating the table.

Syntax:
Describe file_path,

Example:
DESCRIBE 'tests/data/aggregate_simple_pipe.csv';

Return:
column_name data_type is_nullable
c1 Float32 NO
c2 Float64 NO
c3 Boolean NO

Signed-off-by: xyz <a997647204@gmail.com>

Signed-off-by: xyz <a997647204@gmail.com>

Author: xiaoyong-z

datafusion-cli/src/command.rs

@@ -39,7 +39,7 @@ pub enum Command {
     Quit,
     Help,
     ListTables,
-    DescribeTable(String),
+    DescribeTableStmt(String),
     ListFunctions,
     Include(Option<String>),
     SearchFunctions(String),
@@ -65,7 +65,7 @@ impl Command {
                 let batches = df.collect().await?;
                 print_options.print_batches(&batches, now)
             }
-            Self::DescribeTable(name) => {
+            Self::DescribeTableStmt(name) => {
                 let df = ctx.sql(&format!("SHOW COLUMNS FROM {}", name)).await?;
                 let batches = df.collect().await?;
                 print_options.print_batches(&batches, now)
@@ -125,7 +125,7 @@ impl Command {
         match self {
             Self::Quit => ("\\q", "quit datafusion-cli"),
             Self::ListTables => ("\\d", "list tables"),
-            Self::DescribeTable(_) => ("\\d name", "describe table"),
+            Self::DescribeTableStmt(_) => ("\\d name", "describe table"),
             Self::Help => ("\\?", "help"),
             Self::Include(_) => {
                 ("\\i filename", "reads input from the specified filename")
@@ -142,7 +142,7 @@ impl Command {
 
 const ALL_COMMANDS: [Command; 9] = [
     Command::ListTables,
-    Command::DescribeTable(String::new()),
+    Command::DescribeTableStmt(String::new()),
     Command::Quit,
     Command::Help,
     Command::Include(Some(String::new())),
@@ -183,7 +183,7 @@ impl FromStr for Command {
         Ok(match (c, arg) {
             ("q", None) => Self::Quit,
             ("d", None) => Self::ListTables,
-            ("d", Some(name)) => Self::DescribeTable(name.into()),
+            ("d", Some(name)) => Self::DescribeTableStmt(name.into()),
             ("?", None) => Self::Help,
             ("h", None) => Self::ListFunctions,
             ("h", Some(function)) => Self::SearchFunctions(function.into()),

datafusion/core/src/execution/context.rs

@@ -27,6 +27,7 @@ use crate::{
         optimizer::PhysicalOptimizerRule,
     },
 };
+use datafusion_expr::DescribeTable;
 pub use datafusion_physical_expr::execution_props::ExecutionProps;
 use datafusion_physical_expr::var_provider::is_system_variables;
 use parking_lot::RwLock;
@@ -42,8 +43,11 @@ use std::{
 };
 use std::{ops::ControlFlow, sync::Weak};
 
-use arrow::datatypes::{DataType, SchemaRef};
 use arrow::record_batch::RecordBatch;
+use arrow::{
+    array::StringBuilder,
+    datatypes::{DataType, Field, Schema, SchemaRef},
+};
 
 use crate::catalog::{
     catalog::{CatalogProvider, MemoryCatalogProvider},
@@ -360,6 +364,10 @@ impl SessionContext {
                 self.return_empty_dataframe()
             }
 
+            LogicalPlan::DescribeTable(DescribeTable { schema, .. }) => {
+                self.return_describe_table_dataframe(schema).await
+            }
+
             LogicalPlan::CreateCatalogSchema(CreateCatalogSchema {
                 schema_name,
                 if_not_exists,
@@ -442,6 +450,53 @@ impl SessionContext {
         Ok(DataFrame::new(self.state(), plan))
     }
 
+    // return an record_batch which describe table
+    async fn return_describe_table_record_batch(
+        &self,
+        schema: Arc<Schema>,
+    ) -> Result<RecordBatch> {
+        let record_batch_schema = Arc::new(Schema::new(vec![
+            Field::new("column_name", DataType::Utf8, false),
+            Field::new("data_type", DataType::Utf8, false),
+            Field::new("is_nullable", DataType::Utf8, false),
+        ]));
+
+        let mut column_names = StringBuilder::new();
+        let mut data_types = StringBuilder::new();
+        let mut is_nullables = StringBuilder::new();
+        for (_, field) in schema.fields().iter().enumerate() {
+            column_names.append_value(field.name());
+
+            // "System supplied type" --> Use debug format of the datatype
+            let data_type = field.data_type();
+            data_types.append_value(format!("{data_type:?}"));
+
+            // "YES if the column is possibly nullable, NO if it is known not nullable. "
+            let nullable_str = if field.is_nullable() { "YES" } else { "NO" };
+            is_nullables.append_value(nullable_str);
+        }
+
+        let record_batch = RecordBatch::try_new(
+            record_batch_schema,
+            vec![
+                Arc::new(column_names.finish()),
+                Arc::new(data_types.finish()),
+                Arc::new(is_nullables.finish()),
+            ],
+        )?;
+
+        Ok(record_batch)
+    }
+
+    // return an dataframe which describe file
+    async fn return_describe_table_dataframe(
+        &self,
+        schema: Arc<Schema>,
+    ) -> Result<DataFrame> {
+        let record_batch = self.return_describe_table_record_batch(schema).await?;
+        self.read_batch(record_batch)
+    }
+
     async fn create_external_table(
         &self,
         cmd: &CreateExternalTable,
@@ -1719,7 +1774,7 @@ impl SessionState {
             DFStatement::CreateExternalTable(table) => {
                 relations.insert(ObjectName(vec![Ident::from(table.name.as_str())]));
             }
-            DFStatement::DescribeTable(table) => {
+            DFStatement::DescribeTableStmt(table) => {
                 relations
                     .get_or_insert_with(&table.table_name, |_| table.table_name.clone());
             }
@@ -2058,7 +2113,6 @@ mod tests {
     use crate::test_util::parquet_test_data;
     use crate::variable::VarType;
     use arrow::array::ArrayRef;
-    use arrow::datatypes::*;
     use arrow::record_batch::RecordBatch;
     use async_trait::async_trait;
     use datafusion_expr::{create_udaf, create_udf, Expr, Volatility};

datafusion/core/src/physical_plan/planner.rs

@@ -1191,6 +1191,11 @@ impl DefaultPhysicalPlanner {
                         "Unsupported logical plan: SetVariable must be root of the plan".to_string(),
                     ))
                 }
+                LogicalPlan::DescribeTable(_) => {
+                    Err(DataFusionError::Internal(
+                        "Unsupported logical plan: DescribeTable must be root of the plan".to_string(),
+                    ))
+                }
                 LogicalPlan::Explain(_) => Err(DataFusionError::Internal(
                     "Unsupported logical plan: Explain must be root of the plan".to_string(),
                 )),

datafusion/core/tests/sqllogictests/test_files/describe.slt

@@ -0,0 +1,64 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+
+#   http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+
+##########
+# Describe internal tables when information_schema is true
+##########
+
+statement ok
+set datafusion.catalog.information_schema = true
+
+statement ok
+CREATE external table aggregate_simple(c1 real, c2 double, c3 boolean) STORED as CSV WITH HEADER ROW LOCATION 'tests/data/aggregate_simple.csv';
+
+query C1
+DESCRIBE aggregate_simple;
+----
+c1 Float32 NO
+c2 Float64 NO
+c3 Boolean NO
+
+statement ok
+DROP TABLE aggregate_simple;
+
+##########
+# Describe internal tables when information_schema is false
+##########
+
+statement ok
+set datafusion.catalog.information_schema = false
+
+statement ok
+CREATE external table aggregate_simple(c1 real, c2 double, c3 boolean) STORED as CSV WITH HEADER ROW LOCATION 'tests/data/aggregate_simple.csv';
+
+query C2
+DESCRIBE aggregate_simple;
+----
+c1 Float32 NO
+c2 Float64 NO
+c3 Boolean NO
+
+statement ok
+DROP TABLE aggregate_simple;
+
+##########
+# Describe file (currently we can only describe file in datafusion-cli, fix this after issue (#4850) has been done)
+##########
+
+statement error Error during planning: table 'datafusion.public.tests/data/aggregate_simple.csv' not found
+DESCRIBE 'tests/data/aggregate_simple.csv';

datafusion/expr/src/lib.rs

@@ -71,11 +71,12 @@ pub use logical_plan::{
         build_join_schema, union, wrap_projection_for_join_if_necessary, UNNAMED_TABLE,
     },
     Aggregate, CreateCatalog, CreateCatalogSchema, CreateExternalTable,
-    CreateMemoryTable, CreateView, CrossJoin, Distinct, DmlStatement, DropTable,
-    DropView, EmptyRelation, Explain, Extension, Filter, Join, JoinConstraint, JoinType,
-    Limit, LogicalPlan, LogicalPlanBuilder, Partitioning, PlanType, PlanVisitor,
-    Projection, Repartition, SetVariable, Sort, StringifiedPlan, Subquery, SubqueryAlias,
-    TableScan, ToStringifiedPlan, Union, UserDefinedLogicalNode, Values, Window, WriteOp,
+    CreateMemoryTable, CreateView, CrossJoin, DescribeTable, Distinct, DmlStatement,
+    DropTable, DropView, EmptyRelation, Explain, Extension, Filter, Join, JoinConstraint,
+    JoinType, Limit, LogicalPlan, LogicalPlanBuilder, Partitioning, PlanType,
+    PlanVisitor, Projection, Repartition, SetVariable, Sort, StringifiedPlan, Subquery,
+    SubqueryAlias, TableScan, ToStringifiedPlan, Union, UserDefinedLogicalNode, Values,
+    Window, WriteOp,
 };
 pub use nullif::SUPPORTED_NULLIF_TYPES;
 pub use operator::Operator;

datafusion/expr/src/logical_plan/mod.rs

@@ -23,11 +23,11 @@ mod plan;
 pub use builder::{table_scan, LogicalPlanBuilder};
 pub use plan::{
     Aggregate, Analyze, CreateCatalog, CreateCatalogSchema, CreateExternalTable,
-    CreateMemoryTable, CreateView, CrossJoin, Distinct, DmlStatement, DropTable,
-    DropView, EmptyRelation, Explain, Extension, Filter, Join, JoinConstraint, JoinType,
-    Limit, LogicalPlan, Partitioning, PlanType, PlanVisitor, Prepare, Projection,
-    Repartition, SetVariable, Sort, StringifiedPlan, Subquery, SubqueryAlias, TableScan,
-    ToStringifiedPlan, Union, Values, Window, WriteOp,
+    CreateMemoryTable, CreateView, CrossJoin, DescribeTable, Distinct, DmlStatement,
+    DropTable, DropView, EmptyRelation, Explain, Extension, Filter, Join, JoinConstraint,
+    JoinType, Limit, LogicalPlan, Partitioning, PlanType, PlanVisitor, Prepare,
+    Projection, Repartition, SetVariable, Sort, StringifiedPlan, Subquery, SubqueryAlias,
+    TableScan, ToStringifiedPlan, Union, Values, Window, WriteOp,
 };
 
 pub use display::display_schema;

datafusion/expr/src/logical_plan/plan.rs

@@ -121,6 +121,8 @@ pub enum LogicalPlan {
     Prepare(Prepare),
     /// Insert / Update / Delete
     Dml(DmlStatement),
+    /// Describe the schema of table
+    DescribeTable(DescribeTable),
 }
 
 impl LogicalPlan {
@@ -161,6 +163,9 @@ impl LogicalPlan {
             LogicalPlan::DropTable(DropTable { schema, .. }) => schema,
             LogicalPlan::DropView(DropView { schema, .. }) => schema,
             LogicalPlan::SetVariable(SetVariable { schema, .. }) => schema,
+            LogicalPlan::DescribeTable(DescribeTable { dummy_schema, .. }) => {
+                dummy_schema
+            }
             LogicalPlan::Dml(DmlStatement { table_schema, .. }) => table_schema,
         }
     }
@@ -221,6 +226,7 @@ impl LogicalPlan {
             | LogicalPlan::Prepare(Prepare { input, .. }) => input.all_schemas(),
             LogicalPlan::DropTable(_)
             | LogicalPlan::DropView(_)
+            | LogicalPlan::DescribeTable(_)
             | LogicalPlan::SetVariable(_) => vec![],
             LogicalPlan::Dml(DmlStatement { table_schema, .. }) => vec![table_schema],
         }
@@ -322,6 +328,7 @@ impl LogicalPlan {
             | LogicalPlan::Union(_)
             | LogicalPlan::Distinct(_)
             | LogicalPlan::Dml(_)
+            | LogicalPlan::DescribeTable(_)
             | LogicalPlan::Prepare(_) => Ok(()),
         }
     }
@@ -363,7 +370,8 @@ impl LogicalPlan {
             | LogicalPlan::CreateCatalog(_)
             | LogicalPlan::DropTable(_)
             | LogicalPlan::SetVariable(_)
-            | LogicalPlan::DropView(_) => vec![],
+            | LogicalPlan::DropView(_)
+            | LogicalPlan::DescribeTable(_) => vec![],
         }
     }
 
@@ -561,7 +569,8 @@ impl LogicalPlan {
             | LogicalPlan::CreateCatalog(_)
             | LogicalPlan::DropTable(_)
             | LogicalPlan::SetVariable(_)
-            | LogicalPlan::DropView(_) => true,
+            | LogicalPlan::DropView(_)
+            | LogicalPlan::DescribeTable(_) => true,
         };
         if !recurse {
             return Ok(false);
@@ -1170,6 +1179,9 @@ impl LogicalPlan {
                     }) => {
                         write!(f, "Prepare: {name:?} {data_types:?} ")
                     }
+                    LogicalPlan::DescribeTable(DescribeTable { .. }) => {
+                        write!(f, "DescribeTable")
+                    }
                 }
             }
         }
@@ -1625,6 +1637,15 @@ pub struct Prepare {
     pub input: Arc<LogicalPlan>,
 }
 
+/// Describe the schema of table
+#[derive(Clone)]
+pub struct DescribeTable {
+    /// Table schema
+    pub schema: Arc<Schema>,
+    /// Dummy schema
+    pub dummy_schema: DFSchemaRef,
+}
+
 /// Produces a relation with string representations of
 /// various parts of the plan
 #[derive(Clone)]

datafusion/expr/src/utils.rs

@@ -738,6 +738,7 @@ pub fn from_plan(
             assert!(inputs.is_empty(), "{plan:?}  should have no inputs");
             Ok(plan.clone())
         }
+        LogicalPlan::DescribeTable(_) => Ok(plan.clone()),
     }
 }
 

datafusion/optimizer/src/common_subexpr_eliminate.rs

@@ -237,6 +237,7 @@ impl OptimizerRule for CommonSubexprEliminate {
             | LogicalPlan::DropTable(_)
             | LogicalPlan::DropView(_)
             | LogicalPlan::SetVariable(_)
+            | LogicalPlan::DescribeTable(_)
             | LogicalPlan::Distinct(_)
             | LogicalPlan::Extension(_)
             | LogicalPlan::Dml(_)

datafusion/optimizer/src/push_down_projection.rs

@@ -409,6 +409,7 @@ fn optimize_plan(
         | LogicalPlan::DropTable(_)
         | LogicalPlan::DropView(_)
         | LogicalPlan::SetVariable(_)
+        | LogicalPlan::DescribeTable(_)
         | LogicalPlan::CrossJoin(_)
         | LogicalPlan::Dml(_)
         | LogicalPlan::Extension { .. }