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:

PREPARE greater_than(INT) AS SELECT * FROM example WHERE a > $1;

The prepared statement can then be executed with parameters as needed:

EXECUTE greater_than(20);

Rust Example

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

PREPARE greater_than AS SELECT * FROM example WHERE a > $1;

Execute the prepared statement greater_than

EXECUTE greater_than(20);

Rust Example

# 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

PREPARE greater_than(INT, DOUBLE) AS SELECT * FROM example WHERE a > $1 AND b > $2;

Execute the prepared statement greater_than

EXECUTE greater_than(20, 23.3);

Rust Example

# 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(())
# }