Add documentation for prepare statements. (#14639)

* Add documentation for prepare statements.

* Run examples

* Fix heading and example

---------

Co-authored-by: Andrew Lamb <[email protected]>

datafusion/core/src/lib.rs

@@ -962,6 +962,12 @@ doc_comment::doctest!(
     user_guide_sql_operators
 );
 
+#[cfg(doctest)]
+doc_comment::doctest!(
+    "../../../docs/source/user-guide/sql/prepared_statements.md",
+    user_guide_prepared_statements
+);
+
 #[cfg(doctest)]
 doc_comment::doctest!(
     "../../../docs/source/user-guide/sql/scalar_functions.md",

docs/source/user-guide/sql/index.rst

@@ -35,3 +35,4 @@ SQL Reference
    special_functions
    sql_status
    write_options
+   prepared_statements

docs/source/user-guide/sql/prepared_statements.md

@@ -0,0 +1,139 @@
+<!---
+  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.
+-->
+
+# Prepared Statements
+
+The `PREPARE` statement allows for the creation and storage of a SQL statement with placeholder arguments.
+
+The prepared statements can then be executed repeatedly in an efficient manner.
+
+**SQL Example**
+
+Create a prepared statement `greater_than` that selects all records where column "a" is greater than the parameter:
+
+```sql
+PREPARE greater_than(INT) AS SELECT * FROM example WHERE a > $1;
+```
+
+The prepared statement can then be executed with parameters as needed:
+
+```sql
+EXECUTE greater_than(20);
+```
+
+**Rust Example**
+
+```rust
+use datafusion::prelude::*;
+
+#[tokio::main]
+async fn main() -> datafusion::error::Result<()> {
+  // Register the table
+  let ctx = SessionContext::new();
+  ctx.register_csv("example", "tests/data/example.csv", CsvReadOptions::new()).await?;
+
+  // Create the prepared statement `greater_than`
+  let prepare_sql = "PREPARE greater_than(INT) AS SELECT * FROM example WHERE a > $1";
+  ctx.sql(prepare_sql).await?;
+
+  // Execute the prepared statement `greater_than`
+  let execute_sql = "EXECUTE greater_than(20)";
+  let df = ctx.sql(execute_sql).await?;
+
+  // Execute and print results
+  df.show().await?;
+  Ok(())
+}
+```
+
+## Inferred Types
+
+If the parameter type is not specified, it can be inferred at execution time:
+
+**SQL Example**
+
+Create the prepared statement `greater_than`
+
+```sql
+PREPARE greater_than AS SELECT * FROM example WHERE a > $1;
+```
+
+Execute the prepared statement `greater_than`
+
+```sql
+EXECUTE greater_than(20);
+```
+
+**Rust Example**
+
+```rust
+# use datafusion::prelude::*;
+# #[tokio::main]
+# async fn main() -> datafusion::error::Result<()> {
+#    let ctx = SessionContext::new();
+#    ctx.register_csv("example", "tests/data/example.csv", CsvReadOptions::new()).await?;
+#
+    // Create the prepared statement `greater_than`
+    let prepare_sql = "PREPARE greater_than AS SELECT * FROM example WHERE a > $1";
+    ctx.sql(prepare_sql).await?;
+
+    // Execute the prepared statement `greater_than`
+    let execute_sql = "EXECUTE greater_than(20)";
+    let df = ctx.sql(execute_sql).await?;
+#
+#    Ok(())
+# }
+```
+
+## Positional Arguments
+
+In the case of multiple parameters, prepared statements can use positional arguments:
+
+**SQL Example**
+
+Create the prepared statement `greater_than`
+
+```sql
+PREPARE greater_than(INT, DOUBLE) AS SELECT * FROM example WHERE a > $1 AND b > $2;
+```
+
+Execute the prepared statement `greater_than`
+
+```sql
+EXECUTE greater_than(20, 23.3);
+```
+
+**Rust Example**
+
+```rust
+# use datafusion::prelude::*;
+# #[tokio::main]
+# async fn main() -> datafusion::error::Result<()> {
+#    let ctx = SessionContext::new();
+#    ctx.register_csv("example", "tests/data/example.csv", CsvReadOptions::new()).await?;
+  // Create the prepared statement `greater_than`
+  let prepare_sql = "PREPARE greater_than(INT, DOUBLE) AS SELECT * FROM example WHERE a > $1 AND b > $2";
+  ctx.sql(prepare_sql).await?;
+
+  // Execute the prepared statement `greater_than`
+  let execute_sql = "EXECUTE greater_than(20, 23.3)";
+  let df = ctx.sql(execute_sql).await?;
+#    Ok(())
+# }
+```