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new eb3817afdc Example for simple Expr --> SQL conversion (#10528)
eb3817afdc is described below
commit eb3817afdcf25922b09da3d059d1b02bc96be020
Author: Edmondo Porcu <[email protected]>
AuthorDate: Thu May 16 17:32:14 2024 -0700
Example for simple Expr --> SQL conversion (#10528)
* Example for simple conversion
* Fixing example
* Updating README
* Update plan_to_sql.rs
Update file header with more details about the examples
* Fixing formatting
* Update README.md
Fixing extra -
---
datafusion-examples/README.md | 1 +
datafusion-examples/examples/plan_to_sql.rs | 79 +++++++++++++++++++++++++++++
2 files changed, 80 insertions(+)
diff --git a/datafusion-examples/README.md b/datafusion-examples/README.md
index 3e696d6b93..778950cbf9 100644
--- a/datafusion-examples/README.md
+++ b/datafusion-examples/README.md
@@ -63,6 +63,7 @@ cargo run --example csv_sql
- [`parquet_sql.rs`](examples/parquet_sql.rs): Build and run a query plan from
a SQL statement against a local Parquet file
- [`parquet_sql_multiple_files.rs`](examples/parquet_sql_multiple_files.rs):
Build and run a query plan from a SQL statement against multiple local Parquet
files
- ['parquet_exec_visitor.rs'](examples/parquet_exec_visitor.rs): Extract
statistics by visiting an ExecutionPlan after execution
+- [`plan_to_sql.rs`](examples/plan_to_sql.rs): Generate SQL from Datafusion
`Expr` and `LogicalPlan`
- [`pruning.rs`](examples/parquet_sql.rs): Use pruning to rule out files based
on statistics
- [`query-aws-s3.rs`](examples/external_dependency/query-aws-s3.rs): Configure
`object_store` and run a query against files stored in AWS S3
- [`query-http-csv.rs`](examples/query-http-csv.rs): Configure `object_store`
and run a query against files vi HTTP
diff --git a/datafusion-examples/examples/plan_to_sql.rs
b/datafusion-examples/examples/plan_to_sql.rs
new file mode 100644
index 0000000000..3915d3991f
--- /dev/null
+++ b/datafusion-examples/examples/plan_to_sql.rs
@@ -0,0 +1,79 @@
+// 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::*;
+use datafusion::sql::unparser::expr_to_sql;
+use datafusion_sql::unparser::dialect::CustomDialect;
+use datafusion_sql::unparser::Unparser;
+
+/// 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: [`simple_expr_to_sql_demo`]
+/// 3. Create a simple expression [`Exprs`] with fluent API
+/// and convert to sql without escaping column names:
[`simple_expr_to_sql_demo_no_escape`]
+/// 4. Create a simple expression [`Exprs`] with fluent API
+/// and convert to sql escaping column names a MySQL style:
[`simple_expr_to_sql_demo_escape_mysql_style`]
+
+#[tokio::main]
+async fn main() -> Result<()> {
+ // See how to evaluate expressions
+ simple_expr_to_sql_demo()?;
+ simple_expr_to_sql_demo_no_escape()?;
+ simple_expr_to_sql_demo_escape_mysql_style()?;
+ Ok(())
+}
+
+/// DataFusion can convert expressions to SQL, using column name escaping
+/// PostgreSQL style.
+fn simple_expr_to_sql_demo() -> Result<()> {
+ let expr = col("a").lt(lit(5)).or(col("a").eq(lit(8)));
+ let ast = expr_to_sql(&expr)?;
+ let sql = format!("{}", ast);
+ assert_eq!(sql, r#"(("a" < 5) OR ("a" = 8))"#);
+ Ok(())
+}
+
+/// DataFusion can convert expressions to SQL without escaping column names
using
+/// using a custom dialect and an explicit unparser
+fn simple_expr_to_sql_demo_no_escape() -> Result<()> {
+ let expr = col("a").lt(lit(5)).or(col("a").eq(lit(8)));
+ let dialect = CustomDialect::new(None);
+ let unparser = Unparser::new(&dialect);
+ let ast = unparser.expr_to_sql(&expr)?;
+ let sql = format!("{}", ast);
+ assert_eq!(sql, r#"((a < 5) OR (a = 8))"#);
+ Ok(())
+}
+
+/// DataFusion can convert expressions to SQL without escaping column names
using
+/// using a custom dialect and an explicit unparser
+fn simple_expr_to_sql_demo_escape_mysql_style() -> Result<()> {
+ let expr = col("a").lt(lit(5)).or(col("a").eq(lit(8)));
+ let dialect = CustomDialect::new(Some('`'));
+ let unparser = Unparser::new(&dialect);
+ let ast = unparser.expr_to_sql(&expr)?;
+ let sql = format!("{}", ast);
+ assert_eq!(sql, r#"((`a` < 5) OR (`a` = 8))"#);
+ Ok(())
+}
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