remove's gone from the trait ...

... `DROP FUNCTION` will look for function name
in all available registries (udf, udaf, udwf).

`remove` may be necessary if UDaF and UDwF do not
get `simplify` method from #9304.

datafusion/core/src/execution/context/mod.rs

@@ -827,20 +827,23 @@ impl SessionContext {
     }
 
     async fn drop_function(&self, stmt: DropFunction) -> Result<DataFrame> {
-        let _function = {
-            let state = self.state.read().clone();
-            let function_factory = &state.function_factory;
-
-            match function_factory {
-                Some(f) => f.remove(state.config(), stmt).await?,
-                None => Err(DataFusionError::Configuration(
-                    "Function factory has not been configured".into(),
-                ))?,
-            }
-        };
-
-        // TODO: Once we have unregister UDF we need to implement it here
-        self.return_empty_dataframe()
+        // we don't know function type at this point
+        // decision has been made to drop all functions
+        let mut dropped = false;
+        dropped |= self.state.write().deregister_udf(&stmt.name)?.is_some();
+        dropped |= self.state.write().deregister_udaf(&stmt.name)?.is_some();
+        dropped |= self.state.write().deregister_udwf(&stmt.name)?.is_some();
+
+        // DROP FUNCTION IF EXISTS drops the specified function only if that
+        // function exists and in this way, it avoids error. While the DROP FUNCTION
+        // statement also performs the same function, it throws an
+        // error if the function does not exist.
+
+        if !stmt.if_exists && !dropped {
+            Err(DataFusionError::Execution("Function does not exist".into()))
+        } else {
+            self.return_empty_dataframe()
+        }
     }
 
     /// Registers a variable provider within this context.
@@ -1310,18 +1313,9 @@ impl QueryPlanner for DefaultQueryPlanner {
             .await
     }
 }
-/// Crates and registers a function from [CreateFunction] statement
-///
-/// It is intended to handle `CREATE FUNCTION` statements
-/// and interact with [SessionState] to registers new udfs.
-///
-/// Datafusion `SQL` dialect does not support `CREATE FUNCTION`
-/// in generic dialect, so dialect should be changed to `PostgreSQL`
-///
-/// ```rust, no_run
-/// # use datafusion::execution::config::SessionConfig;
-/// SessionConfig::new().set_str("datafusion.sql_parser.dialect", "PostgreSQL");
-/// ```
+/// A pluggable interface to handle `CREATE FUNCTION` statements
+/// and interact with [SessionState] to registers new udf, udaf or udwf.
+
 #[async_trait]
 pub trait FunctionFactory: Sync + Send {
     /// Handles creation of user defined function specified in [CreateFunction] statement
@@ -1330,14 +1324,6 @@ pub trait FunctionFactory: Sync + Send {
         state: &SessionConfig,
         statement: CreateFunction,
     ) -> Result<RegisterFunction>;
-
-    /// Drops user defined function from [SessionState]
-    // Naming it `drop` would make more sense but its already occupied in rust
-    async fn remove(
-        &self,
-        state: &SessionConfig,
-        statement: DropFunction,
-    ) -> Result<RegisterFunction>;
 }
 
 /// Type of function to create

datafusion/core/tests/user_defined/user_defined_scalar_functions.rs

@@ -31,8 +31,8 @@ use datafusion_common::{
 };
 use datafusion_execution::runtime_env::{RuntimeConfig, RuntimeEnv};
 use datafusion_expr::{
-    create_udaf, create_udf, Accumulator, ColumnarValue, CreateFunction, DropFunction,
-    ExprSchemable, LogicalPlanBuilder, ScalarUDF, ScalarUDFImpl, Signature, Volatility,
+    create_udaf, create_udf, Accumulator, ColumnarValue, CreateFunction, ExprSchemable,
+    LogicalPlanBuilder, ScalarUDF, ScalarUDFImpl, Signature, Volatility,
 };
 use parking_lot::Mutex;
 use rand::{thread_rng, Rng};
@@ -693,28 +693,10 @@ impl FunctionFactory for MockFunctionFactory {
 
         Ok(RegisterFunction::Scalar(Arc::new(mock_udf)))
     }
-
-    async fn remove(
-        &self,
-        _config: &SessionConfig,
-        _statement: DropFunction,
-    ) -> datafusion::error::Result<RegisterFunction> {
-        // TODO: I don't like that remove returns RegisterFunction
-        //       we have to keep two states in FunctionFactory iml and
-        //       SessionState
-        //
-        //      It would be better to return (function_name, function type) tuple
-        //
-        // at the moment state does not support unregister user defined functions
-
-        Err(datafusion_common::DataFusionError::NotImplemented(
-            "remove function has not been implemented".into(),
-        ))
-    }
 }
 
 #[tokio::test]
-async fn create_scalar_function_from_sql_statement() {
+async fn create_scalar_function_from_sql_statement() -> Result<()> {
     let function_factory = Arc::new(MockFunctionFactory::default());
     let runtime_config = RuntimeConfig::new();
     let runtime_environment = RuntimeEnv::new(runtime_config).unwrap();
@@ -732,23 +714,26 @@ async fn create_scalar_function_from_sql_statement() {
         RETURNS DOUBLE
         RETURN $1 + $2
     "#;
-    let _ = ctx.sql(sql).await.unwrap();
+    let _ = ctx.sql(sql).await?;
 
-    ctx.sql("select better_add(2.0, 2.0)")
-        .await
-        .unwrap()
-        .show()
-        .await
-        .unwrap();
+    ctx.sql("select better_add(2.0, 2.0)").await?.show().await?;
 
     // check if we sql expr has been converted to datafusion expr
     let captured_expression = function_factory.captured_expr.lock().clone().unwrap();
 
     // is there some better way to test this
     assert_eq!("$1 + $2", captured_expression.to_string());
 
-    // no support at the moment
-    // ctx.sql("drop function better_add").await.unwrap();
+    // statement drops  function
+    assert!(ctx.sql("drop function better_add").await.is_ok());
+    // no function, it panics
+    assert!(ctx.sql("drop function better_add").await.is_err());
+    // no function, it dies not care
+    assert!(ctx.sql("drop function if exists better_add").await.is_ok());
+    // query should fail as there is no function
+    assert!(ctx.sql("select better_add(2.0, 2.0)").await.is_err());
+
+    Ok(())
 }
 
 fn create_udf_context() -> SessionContext {