Example for simple Expr --> SQL conversion

datafusion-examples/examples/plan_to_sql.rs

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+// 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 datafusion::error::Result;
+
+use datafusion::prelude::*;
+
+/// This example demonstrates the programmatic construction of
+/// SQL using the DataFusion Expr [`Expr`] and LogicalPlan [`LogicalPlan`] API.
+///
+///
+/// The code in this example shows how to:
+/// 1. Create SQL from a variety of Expr and LogicalPlan: [`main`]`
+/// 2. Create a simple expression [`Exprs`] with fluent API
+/// and convert to sql against data: [`simple_expr_to_sql_demo`]
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    // See how to evaluate expressions
+    simple_expr_to_sql_demo();
+
+    Ok(())
+}
+
+/// DataFusion can convert expressions to SQL
+fn simple_expr_to_sql_demo() {
+    let expr = col("a").lt(lit(5)).or(col("a").eq(lit(8)));
+    let sql = expr.to_string();
+    assert_eq!(sql, "a < 5 OR a = 8");
+}