alamb commented on code in PR #3741:
URL: https://github.com/apache/arrow-datafusion/pull/3741#discussion_r993591865
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datafusion/core/src/prelude.rs:
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@@ -34,7 +34,7 @@ pub use crate::execution::options::{
pub use datafusion_common::Column;
pub use datafusion_expr::{
expr_fn::*,
- lit,
+ lit, lit_timestamp_nano,
Review Comment:
driveby fix
##########
datafusion-examples/examples/expr_api.rs:
##########
@@ -0,0 +1,136 @@
+// 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::arrow::datatypes::{DataType, Field, Schema, TimeUnit};
+
+use datafusion::error::Result;
+use datafusion::logical_plan::ToDFSchema;
+use datafusion::optimizer::expr_simplifier::{ExprSimplifier, SimplifyContext};
+use datafusion::physical_expr::execution_props::ExecutionProps;
+use datafusion::prelude::*;
+use datafusion::{logical_plan::Operator, scalar::ScalarValue};
+
+/// This example demonstrates the DataFusion [`Expr`] API.
+///
+/// DataFusion comes with a powerful and extensive system for
+/// representing and manipulating expressions such as `A + 5` and `X
+/// IN ('foo', 'bar', 'baz')` and many other constructs.
+
+#[tokio::main]
+async fn main() -> Result<()> {
+ // The easiest way to do create expressions is to use the
+ // "fluent"-style API, like this:
+ let expr = col("a") + lit(5);
+
+ // this creates the same expression as the following though with
+ // much less code,
+ let expr2 = Expr::BinaryExpr {
+ left: Box::new(col("a")),
+ op: Operator::Plus,
+ right: Box::new(Expr::Literal(ScalarValue::Int32(Some(5)))),
+ };
+ assert_eq!(expr, expr2);
+
+ simplify_demo()?;
+
+ Ok(())
+}
+
+/// In addition to easy construction, DataFusion exposes APIs for
+/// working with and simplifying such expressions that call into the
+/// same powerful and extensive implementation used for the query
+/// engine.
+fn simplify_demo() -> Result<()> {
+ // For example, lets say you have has created an expression such
+ // ts = to_timestamp("2020-09-08T12:00:00+00:00")
+ let expr = col("ts").eq(call_fn(
+ "to_timestamp",
+ vec![lit("2020-09-08T12:00:00+00:00")],
+ )?);
+
+ // Naively evaluating such an expression against a large number of
+ // rows would involve re-converting "2020-09-08T12:00:00+00:00" to a
+ // timestamp for each row which gets expensive
+ //
+ // However, DataFusion's simplification logic can do this for you
+
+ // you need to tell DataFusion the type of column "ts":
+ let schema = Schema::new(vec![make_ts_field("ts")]).to_dfschema_ref()?;
+
+ // And then build a simplifier
+ // the ExecutionProps carries information needed to simplify
+ // expressions, such as the current time (to evaluate `now()`
+ // correctly)
+ let props = ExecutionProps::new();
+ let context = SimplifyContext::new(&props).with_schema(schema);
+ let simplifier = ExprSimplifier::new(context);
+
+ // And then call the simplify_expr function:
+ let expr = simplifier.simplify(expr)?;
+
+ // DataFusion has simplified the expression to a comparison with a constant
+ // ts = 1599566400000000000; Tada!
+ assert_eq!(
+ expr,
+ col("ts").eq(lit_timestamp_nano(1599566400000000000i64))
+ );
+
+ // here are some other examples of what DataFusion is capable of
+ let schema = Schema::new(vec![
+ make_field("i", DataType::Int64),
+ make_field("b", DataType::Boolean),
+ ])
+ .to_dfschema_ref()?;
+ let context = SimplifyContext::new(&props).with_schema(schema);
+ let simplifier = ExprSimplifier::new(context);
+
+ // basic arithmetic simplification
+ // i + 1 + 2 => a + 3
+ // (note this is not done if the expr is (col("i") + (lit(1) + lit(2))))
+ assert_eq!(
+ simplifier.simplify(col("i") + (lit(1) + lit(2)))?,
+ col("i") + lit(3)
+ );
+
+ // TODO uncomment when
https://github.com/apache/arrow-datafusion/issues/1160 is done
Review Comment:
I will do a partial fix for this in a follow on PR
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