Implement SHOW FUNCTIONS

datafusion/core/tests/sql/mod.rs

@@ -62,6 +62,7 @@ pub mod explain_analyze;
 pub mod joins;
 mod path_partition;
 pub mod select;
+pub mod show;
 mod sql_api;
 
 async fn register_aggregate_csv_by_sql(ctx: &SessionContext) {

datafusion/core/tests/sql/show.rs

@@ -0,0 +1,45 @@
+// 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.
+
+use super::*;
+use std::collections::HashSet;
+
+#[tokio::test]
+async fn test_show_functions() {
+    let ctx = SessionContext::new();
+    let result = execute(&ctx, "SHOW FUNCTIONS").await;
+    println!("{:?}", result);
+    assert!(!result.is_empty(), "result is empty");
+    let names: HashSet<String> = result
+        .into_iter()
+        .map(|mut row| {
+            assert_eq!(row.len(), 1);
+            row.remove(0)
+        })
+        .collect();
+    [
+        "array_distinct",
+        "to_unixtime",
+        "covar_pop",
+        "max",
+        "concat",
+    ]
+    .into_iter()
+    .for_each(|name| {
+        assert!(names.contains(name), "{} not found in {:?}", name, names);
+    });
+}

datafusion/sql/src/statement.rs

@@ -15,7 +15,8 @@
 // specific language governing permissions and limitations
 // under the License.
 
-use std::collections::{BTreeMap, HashMap, HashSet};
+use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet};
+use std::iter;
 use std::path::Path;
 use std::str::FromStr;
 use std::sync::Arc;
@@ -29,7 +30,7 @@ use crate::planner::{
 };
 use crate::utils::normalize_ident;
 
-use arrow_schema::{DataType, Fields};
+use arrow_schema::{DataType, Field, Fields, Schema};
 use datafusion_common::parsers::CompressionTypeVariant;
 use datafusion_common::{
     exec_err, not_impl_err, plan_datafusion_err, plan_err, schema_err,
@@ -43,15 +44,15 @@ use datafusion_expr::logical_plan::builder::project;
 use datafusion_expr::logical_plan::DdlStatement;
 use datafusion_expr::utils::expr_to_columns;
 use datafusion_expr::{
-    cast, col, Analyze, CreateCatalog, CreateCatalogSchema,
+    cast, col, lit, Analyze, BuiltInWindowFunction, CreateCatalog, CreateCatalogSchema,
     CreateExternalTable as PlanCreateExternalTable, CreateFunction, CreateFunctionBody,
     CreateIndex as PlanCreateIndex, CreateMemoryTable, CreateView, DescribeTable,
     DmlStatement, DropCatalogSchema, DropFunction, DropTable, DropView, EmptyRelation,
     Explain, Expr, ExprSchemable, Filter, LogicalPlan, LogicalPlanBuilder,
     OperateFunctionArg, PlanType, Prepare, SetVariable, SortExpr,
     Statement as PlanStatement, ToStringifiedPlan, TransactionAccessMode,
     TransactionConclusion, TransactionEnd, TransactionIsolationLevel, TransactionStart,
-    Volatility, WriteOp,
+    Values, Volatility, WriteOp,
 };
 use sqlparser::ast;
 use sqlparser::ast::{
@@ -62,6 +63,7 @@ use sqlparser::ast::{
     TableWithJoins, TransactionMode, UnaryOperator, Value,
 };
 use sqlparser::parser::ParserError::ParserError;
+use strum::IntoEnumIterator;
 
 fn ident_to_string(ident: &Ident) -> String {
     normalize_ident(ident.to_owned())
@@ -469,6 +471,8 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
                 filter,
             } => self.show_columns_to_plan(extended, full, table_name, filter),
 
+            Statement::ShowFunctions { filter } => self.show_functions_to_plan(filter),
+
             Statement::Insert(Insert {
                 or,
                 into,
@@ -1588,6 +1592,37 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
         self.statement_to_plan(rewrite.pop_front().unwrap()) // length of rewrite is 1
     }
 
+    fn show_functions_to_plan(
+        &self,
+        filter: Option<ShowStatementFilter>,
+    ) -> Result<LogicalPlan> {
+        if filter.is_some() {
+            // See https://github.com/sqlparser-rs/sqlparser-rs/issues/1399 before adding support for filter.
+            return plan_err!("SHOW FUNCTIONS with WHERE or LIKE is not supported");
+        }
+
+        let names = iter::empty::<String>()
+            .chain(self.context_provider.udf_names())
+            .chain(self.context_provider.udaf_names())
+            .chain(BuiltInWindowFunction::iter().map(|func| func.to_string()))
+            .chain(self.context_provider.udwf_names())
+            // TODO list table functions
+            .map(|name| name.to_lowercase())
+            .collect::<BTreeSet<_>>();
+
+        Ok(LogicalPlan::Values(Values {
+            schema: Arc::new(
+                DFSchema::try_from(Schema::new(vec![Field::new(
+                    "function_name",
+                    DataType::Utf8,
+                    false,
+                )]))
+                .unwrap(),
+            ),
+            values: names.into_iter().map(|name| vec![lit(name)]).collect(),
+        }))
+    }
+
     /// Return true if there is a table provider available for "schema.table"
     fn has_table(&self, schema: &str, table: &str) -> bool {
         let tables_reference = TableReference::Partial {