feat: support function aliases and add MySQL-compatible aliases (#7410)

* feat: support function aliases and add MySQL-compatible aliases

Signed-off-by: Dennis Zhuang <killme2008@gmail.com>

* fix: get_table_function_source

Signed-off-by: Dennis Zhuang <killme2008@gmail.com>

* refactor: add function_alias mod

Signed-off-by: Dennis Zhuang <killme2008@gmail.com>

* fix: license

Signed-off-by: Dennis Zhuang <killme2008@gmail.com>

---------

Signed-off-by: Dennis Zhuang <killme2008@gmail.com>

src/query/src/datafusion/planner.rs

@@ -41,6 +41,8 @@ use snafu::{Location, ResultExt};
 use crate::error::{CatalogSnafu, Result};
 use crate::query_engine::{DefaultPlanDecoder, QueryEngineState};
 
+mod function_alias;
+
 pub struct DfContextProviderAdapter {
     engine_state: Arc<QueryEngineState>,
     session_state: SessionState,
@@ -147,7 +149,17 @@ impl ContextProvider for DfContextProviderAdapter {
 
     fn get_function_meta(&self, name: &str) -> Option<Arc<ScalarUDF>> {
         self.engine_state.scalar_function(name).map_or_else(
-            || self.session_state.scalar_functions().get(name).cloned(),
+            || {
+                self.session_state
+                    .scalar_functions()
+                    .get(name)
+                    .cloned()
+                    .or_else(|| {
+                        function_alias::resolve_scalar(name).and_then(|name| {
+                            self.session_state.scalar_functions().get(name).cloned()
+                        })
+                    })
+            },
             |func| {
                 Some(Arc::new(func.provide(FunctionContext {
                     query_ctx: self.query_ctx.clone(),
@@ -159,7 +171,17 @@ impl ContextProvider for DfContextProviderAdapter {
 
     fn get_aggregate_meta(&self, name: &str) -> Option<Arc<AggregateUDF>> {
         self.engine_state.aggr_function(name).map_or_else(
-            || self.session_state.aggregate_functions().get(name).cloned(),
+            || {
+                self.session_state
+                    .aggregate_functions()
+                    .get(name)
+                    .cloned()
+                    .or_else(|| {
+                        function_alias::resolve_aggregate(name).and_then(|name| {
+                            self.session_state.aggregate_functions().get(name).cloned()
+                        })
+                    })
+            },
             |func| Some(Arc::new(func)),
         )
     }
@@ -193,12 +215,14 @@ impl ContextProvider for DfContextProviderAdapter {
     fn udf_names(&self) -> Vec<String> {
         let mut names = self.engine_state.scalar_names();
         names.extend(self.session_state.scalar_functions().keys().cloned());
+        names.extend(function_alias::scalar_alias_names().map(|name| name.to_string()));
         names
     }
 
     fn udaf_names(&self) -> Vec<String> {
         let mut names = self.engine_state.aggr_names();
         names.extend(self.session_state.aggregate_functions().keys().cloned());
+        names.extend(function_alias::aggregate_alias_names().map(|name| name.to_string()));
         names
     }
 
@@ -233,9 +257,14 @@ impl ContextProvider for DfContextProviderAdapter {
                 .table_functions()
                 .get(name)
                 .cloned()
-                .ok_or_else(|| {
-                    DataFusionError::Plan(format!("table function '{name}' not found"))
-                })?;
+                .or_else(|| {
+                    function_alias::resolve_scalar(name)
+                        .and_then(|alias| self.session_state.table_functions().get(alias).cloned())
+                });
+
+            let tbl_func = tbl_func.ok_or_else(|| {
+                DataFusionError::Plan(format!("table function '{name}' not found"))
+            })?;
             let provider = tbl_func.create_table_provider(&args)?;
 
             Ok(provider_as_source(provider))

src/query/src/datafusion/planner/function_alias.rs

@@ -0,0 +1,86 @@
+// Copyright 2023 Greptime Team
+//
+// Licensed 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 std::collections::HashMap;
+
+use once_cell::sync::Lazy;
+
+const SCALAR_ALIASES: &[(&str, &str)] = &[
+    // SQL compat aliases.
+    ("ucase", "upper"),
+    ("lcase", "lower"),
+    ("ceiling", "ceil"),
+    ("mid", "substr"),
+    // MySQL's RAND([seed]) accepts an optional seed argument, while DataFusion's `random()`
+    // does not. We alias the name for `rand()` compatibility, and `rand(seed)` will error
+    // due to mismatched arity.
+    ("rand", "random"),
+];
+
+const AGGREGATE_ALIASES: &[(&str, &str)] = &[
+    // MySQL compat aliases that don't override existing DataFusion aggregate names.
+    //
+    // NOTE: We intentionally do NOT alias `stddev` here, because DataFusion defines `stddev`
+    // as sample standard deviation while MySQL's `STDDEV` is population standard deviation.
+    ("std", "stddev_pop"),
+    ("variance", "var_pop"),
+];
+
+static SCALAR_FUNCTION_ALIAS: Lazy<HashMap<&'static str, &'static str>> =
+    Lazy::new(|| SCALAR_ALIASES.iter().copied().collect());
+
+static AGGREGATE_FUNCTION_ALIAS: Lazy<HashMap<&'static str, &'static str>> =
+    Lazy::new(|| AGGREGATE_ALIASES.iter().copied().collect());
+
+pub fn resolve_scalar(name: &str) -> Option<&'static str> {
+    let name = name.to_ascii_lowercase();
+    SCALAR_FUNCTION_ALIAS.get(name.as_str()).copied()
+}
+
+pub fn resolve_aggregate(name: &str) -> Option<&'static str> {
+    let name = name.to_ascii_lowercase();
+    AGGREGATE_FUNCTION_ALIAS.get(name.as_str()).copied()
+}
+
+pub fn scalar_alias_names() -> impl Iterator<Item = &'static str> {
+    SCALAR_ALIASES.iter().map(|(name, _)| *name)
+}
+
+pub fn aggregate_alias_names() -> impl Iterator<Item = &'static str> {
+    AGGREGATE_ALIASES.iter().map(|(name, _)| *name)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{resolve_aggregate, resolve_scalar};
+
+    #[test]
+    fn resolves_scalar_aliases_case_insensitive() {
+        assert_eq!(resolve_scalar("ucase"), Some("upper"));
+        assert_eq!(resolve_scalar("UCASE"), Some("upper"));
+        assert_eq!(resolve_scalar("lcase"), Some("lower"));
+        assert_eq!(resolve_scalar("ceiling"), Some("ceil"));
+        assert_eq!(resolve_scalar("MID"), Some("substr"));
+        assert_eq!(resolve_scalar("RAND"), Some("random"));
+        assert_eq!(resolve_scalar("not_a_real_alias"), None);
+    }
+
+    #[test]
+    fn resolves_aggregate_aliases_case_insensitive() {
+        assert_eq!(resolve_aggregate("std"), Some("stddev_pop"));
+        assert_eq!(resolve_aggregate("variance"), Some("var_pop"));
+        assert_eq!(resolve_aggregate("STDDEV"), None);
+        assert_eq!(resolve_aggregate("not_a_real_alias"), None);
+    }
+}

tests/cases/standalone/common/function/function_alias.result

@@ -0,0 +1,72 @@
+-- MySQL-compatible function alias tests
+-- ucase -> upper
+SELECT
+    ucase('dataFusion') AS ucase_value,
+    upper('dataFusion') AS upper_value;
+
++-------------+-------------+
+| ucase_value | upper_value |
++-------------+-------------+
+| DATAFUSION  | DATAFUSION  |
++-------------+-------------+
+
+-- lcase -> lower
+SELECT
+    lcase('DataFusion') AS lcase_value,
+    lower('DataFusion') AS lower_value;
+
++-------------+-------------+
+| lcase_value | lower_value |
++-------------+-------------+
+| datafusion  | datafusion  |
++-------------+-------------+
+
+-- ceiling -> ceil
+SELECT
+    ceiling(1.2) AS ceiling_pos,
+    ceil(1.2) AS ceil_pos,
+    ceiling(-1.2) AS ceiling_neg,
+    ceil(-1.2) AS ceil_neg;
+
++-------------+----------+-------------+----------+
+| ceiling_pos | ceil_pos | ceiling_neg | ceil_neg |
++-------------+----------+-------------+----------+
+| 2.0         | 2.0      | -1.0        | -1.0     |
++-------------+----------+-------------+----------+
+
+-- mid -> substr
+SELECT
+    mid('datafusion', 5, 3) AS mid_value,
+    substr('datafusion', 5, 3) AS substr_value;
+
++-----------+--------------+
+| mid_value | substr_value |
++-----------+--------------+
+| fus       | fus          |
++-----------+--------------+
+
+-- rand -> random
+-- NOTE: RAND([seed]) is supported by MySQL, but seed is not supported here.
+-- This test only validates that rand() exists and returns values in [0, 1).
+SELECT rand() >= 0.0 AND rand() < 1.0 AS rand_in_range;
+
++---------------+
+| rand_in_range |
++---------------+
+| true          |
++---------------+
+
+-- std -> stddev_pop, variance -> var_pop
+SELECT
+    round(std(x), 6) AS std_value,
+    round(stddev_pop(x), 6) AS stddev_pop_value,
+    round(variance(x), 6) AS variance_value,
+    round(var_pop(x), 6) AS var_pop_value
+FROM (VALUES (1.0), (2.0), (3.0)) AS t(x);
+
++-----------+------------------+----------------+---------------+
+| std_value | stddev_pop_value | variance_value | var_pop_value |
++-----------+------------------+----------------+---------------+
+| 0.816497  | 0.816497         | 0.666667       | 0.666667      |
++-----------+------------------+----------------+---------------+
+

tests/cases/standalone/common/function/function_alias.sql

@@ -0,0 +1,36 @@
+-- MySQL-compatible function alias tests
+
+-- ucase -> upper
+SELECT
+    ucase('dataFusion') AS ucase_value,
+    upper('dataFusion') AS upper_value;
+
+-- lcase -> lower
+SELECT
+    lcase('DataFusion') AS lcase_value,
+    lower('DataFusion') AS lower_value;
+
+-- ceiling -> ceil
+SELECT
+    ceiling(1.2) AS ceiling_pos,
+    ceil(1.2) AS ceil_pos,
+    ceiling(-1.2) AS ceiling_neg,
+    ceil(-1.2) AS ceil_neg;
+
+-- mid -> substr
+SELECT
+    mid('datafusion', 5, 3) AS mid_value,
+    substr('datafusion', 5, 3) AS substr_value;
+
+-- rand -> random
+-- NOTE: RAND([seed]) is supported by MySQL, but seed is not supported here.
+-- This test only validates that rand() exists and returns values in [0, 1).
+SELECT rand() >= 0.0 AND rand() < 1.0 AS rand_in_range;
+
+-- std -> stddev_pop, variance -> var_pop
+SELECT
+    round(std(x), 6) AS std_value,
+    round(stddev_pop(x), 6) AS stddev_pop_value,
+    round(variance(x), 6) AS variance_value,
+    round(var_pop(x), 6) AS var_pop_value
+FROM (VALUES (1.0), (2.0), (3.0)) AS t(x);