From 9400c180706e0707b0ad99d11d9134392bc42706 Mon Sep 17 00:00:00 2001
From: nobigo <nobigogle@gmail.com>
Date: Tue, 10 Sep 2024 19:07:26 +0800
Subject: [PATCH 1/5] [CALCITE-6566] JDBC adapter should generate PI function
 with parentheses When unparse PI function without parentheses

---
 .../apache/calcite/sql/SqlBasicFunction.java  | 11 +++++++++
 .../java/org/apache/calcite/sql/SqlKind.java  |  3 +++
 .../sql/dialect/ClickHouseSqlDialect.java     |  4 ++++
 .../calcite/sql/dialect/HiveSqlDialect.java   |  3 +++
 .../calcite/sql/dialect/MssqlSqlDialect.java  |  5 +++-
 .../calcite/sql/dialect/MysqlSqlDialect.java  |  7 +++---
 .../sql/dialect/PostgresqlSqlDialect.java     |  4 ++++
 .../calcite/sql/dialect/PrestoSqlDialect.java |  3 +++
 .../calcite/sql/dialect/SparkSqlDialect.java  |  4 ++++
 .../calcite/sql/fun/SqlStdOperatorTable.java  |  2 +-
 .../calcite/util/RelToSqlConverterUtil.java   | 21 +++++++++++++++++
 .../rel/rel2sql/RelToSqlConverterTest.java    | 23 +++++++++++++++++++
 12 files changed, 85 insertions(+), 5 deletions(-)

diff --git a/core/src/main/java/org/apache/calcite/sql/SqlBasicFunction.java b/core/src/main/java/org/apache/calcite/sql/SqlBasicFunction.java
index 05c1f80c0b6..c60aebede69 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlBasicFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlBasicFunction.java
@@ -107,6 +107,17 @@ public static SqlBasicFunction create(String name, SqlKind kind,
         SqlFunctionCategory.SYSTEM, call -> SqlMonotonicity.NOT_MONOTONIC, false);
   }
 
+  /** Creates a {@code SqlBasicFunction} whose name is the same as its kind. */
+  public static SqlBasicFunction create(SqlKind kind,
+      SqlReturnTypeInference returnTypeInference,
+      SqlOperandTypeChecker operandTypeChecker,
+      SqlFunctionCategory category) {
+    return new SqlBasicFunction(kind.name(), kind,
+        SqlSyntax.FUNCTION, true, returnTypeInference, null,
+        OperandHandlers.DEFAULT, operandTypeChecker, 0,
+        category, call -> SqlMonotonicity.NOT_MONOTONIC, false);
+  }
+
   /** Creates a {@code SqlBasicFunction} whose name is the same as its kind
    * and whose category {@link SqlFunctionCategory#SYSTEM}. */
   public static SqlBasicFunction create(SqlKind kind,
diff --git a/core/src/main/java/org/apache/calcite/sql/SqlKind.java b/core/src/main/java/org/apache/calcite/sql/SqlKind.java
index 70094d1b49d..62088f31407 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlKind.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlKind.java
@@ -731,6 +731,9 @@ public enum SqlKind {
   /** {@code CEIL} function. */
   CEIL,
 
+  /** ${code PI} function. */
+  PI,
+
   /** {@code TRIM} function. */
   TRIM,
 
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/ClickHouseSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/ClickHouseSqlDialect.java
index 9fc3618924b..5e43267ccb8 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/ClickHouseSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/ClickHouseSqlDialect.java
@@ -33,6 +33,7 @@
 import org.apache.calcite.sql.parser.SqlParserPos;
 import org.apache.calcite.sql.type.BasicSqlType;
 import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.util.RelToSqlConverterUtil;
 
 import org.checkerframework.checker.nullness.qual.Nullable;
 
@@ -203,6 +204,9 @@ private static SqlDataTypeSpec createSqlDataTypeSpecByName(String typeAlias,
       call.operand(1).unparse(writer, 0, 0);
       writer.endList(frame);
       break;
+    case PI:
+      RelToSqlConverterUtil.unparsePI(writer, call, leftPrec, rightPrec);
+      break;
     default:
       super.unparseCall(writer, call, leftPrec, rightPrec);
     }
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/HiveSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/HiveSqlDialect.java
index bf40da483e7..ac1bbcadf60 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/HiveSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/HiveSqlDialect.java
@@ -109,6 +109,9 @@ public HiveSqlDialect(Context context) {
     case TRIM:
       RelToSqlConverterUtil.unparseHiveTrim(writer, call, leftPrec, rightPrec);
       break;
+    case PI:
+      RelToSqlConverterUtil.unparsePI(writer, call, leftPrec, rightPrec);
+      break;
     default:
       super.unparseCall(writer, call, leftPrec, rightPrec);
     }
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/MssqlSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/MssqlSqlDialect.java
index 6f32a33a4a9..c7ebb668eb3 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/MssqlSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/MssqlSqlDialect.java
@@ -40,6 +40,7 @@
 import org.apache.calcite.sql.type.OperandTypes;
 import org.apache.calcite.sql.type.ReturnTypes;
 import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.util.RelToSqlConverterUtil;
 
 import org.checkerframework.checker.nullness.qual.Nullable;
 
@@ -172,7 +173,9 @@ public MssqlSqlDialect(Context context) {
         }
         unparseFloor(writer, call);
         break;
-
+      case PI:
+        RelToSqlConverterUtil.unparsePI(writer, call, leftPrec, rightPrec);
+        break;
       default:
         super.unparseCall(writer, call, leftPrec, rightPrec);
       }
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/MysqlSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/MysqlSqlDialect.java
index fc2a7a1b054..1aa27d8993b 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/MysqlSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/MysqlSqlDialect.java
@@ -48,6 +48,7 @@
 import org.apache.calcite.sql.type.OperandTypes;
 import org.apache.calcite.sql.type.ReturnTypes;
 import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.util.RelToSqlConverterUtil;
 
 import com.google.common.collect.ImmutableList;
 
@@ -242,7 +243,6 @@ public MysqlSqlDialect(Context context) {
 
       unparseFloor(writer, call);
       break;
-
     case WITHIN_GROUP:
       final List<SqlNode> operands = call.getOperandList();
       if (operands.size() <= 0 || operands.get(0).getKind() != SqlKind.LISTAGG) {
@@ -252,11 +252,12 @@ public MysqlSqlDialect(Context context) {
       unparseListAggCall(writer, (SqlCall) operands.get(0),
           operands.size() == 2 ? operands.get(1) : null, leftPrec, rightPrec);
       break;
-
     case LISTAGG:
       unparseListAggCall(writer, call, null, leftPrec, rightPrec);
       break;
-
+    case PI:
+      RelToSqlConverterUtil.unparsePI(writer, call, leftPrec, rightPrec);
+      break;
     default:
       super.unparseCall(writer, call, leftPrec, rightPrec);
     }
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/PostgresqlSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/PostgresqlSqlDialect.java
index 627b3c79a41..c2eba8aac98 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/PostgresqlSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/PostgresqlSqlDialect.java
@@ -38,6 +38,7 @@
 import org.apache.calcite.sql.fun.SqlStdOperatorTable;
 import org.apache.calcite.sql.parser.SqlParserPos;
 import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.util.RelToSqlConverterUtil;
 
 import com.google.common.collect.ImmutableList;
 
@@ -177,6 +178,9 @@ public PostgresqlSqlDialect(Context context) {
               timeUnitNode.getParserPosition());
       SqlFloorFunction.unparseDatetimeFunction(writer, call2, "DATE_TRUNC", false);
       break;
+    case PI:
+      RelToSqlConverterUtil.unparsePI(writer, call, leftPrec, rightPrec);
+      break;
     default:
       super.unparseCall(writer, call, leftPrec, rightPrec);
     }
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/PrestoSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/PrestoSqlDialect.java
index 4b6c7c3292d..961870cb464 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/PrestoSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/PrestoSqlDialect.java
@@ -145,6 +145,9 @@ private static void unparseUsingLimit(SqlWriter writer, @Nullable SqlNode offset
       case MAP_VALUE_CONSTRUCTOR:
         unparseMapValue(writer, call, leftPrec, rightPrec);
         break;
+      case PI:
+        RelToSqlConverterUtil.unparsePI(writer, call, leftPrec, rightPrec);
+        break;
       default:
         // Current impl is same with Postgresql.
         PostgresqlSqlDialect.DEFAULT.unparseCall(writer, call, leftPrec, rightPrec);
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/SparkSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/SparkSqlDialect.java
index c2daf0ab677..c8e0254b069 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/SparkSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/SparkSqlDialect.java
@@ -34,6 +34,7 @@
 import org.apache.calcite.sql.parser.SqlParserPos;
 import org.apache.calcite.sql.type.BasicSqlType;
 import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.calcite.util.RelToSqlConverterUtil;
 
 import org.checkerframework.checker.nullness.qual.Nullable;
 
@@ -139,6 +140,9 @@ public SparkSqlDialect(SqlDialect.Context context) {
     case POSITION:
       SqlUtil.unparseFunctionSyntax(SqlStdOperatorTable.POSITION, writer, call, false);
       break;
+    case PI:
+      RelToSqlConverterUtil.unparsePI(writer, call, leftPrec, rightPrec);
+      break;
     default:
       super.unparseCall(writer, call, leftPrec, rightPrec);
     }
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlStdOperatorTable.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlStdOperatorTable.java
index 0254e2a219b..0ab0a240b16 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlStdOperatorTable.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlStdOperatorTable.java
@@ -1815,7 +1815,7 @@ public class SqlStdOperatorTable extends ReflectiveSqlOperatorTable {
 
   /** The {@code PI} function. */
   public static final SqlFunction PI =
-      SqlBasicFunction.create("PI", ReturnTypes.DOUBLE, OperandTypes.NILADIC,
+      SqlBasicFunction.create(SqlKind.PI, ReturnTypes.DOUBLE, OperandTypes.NILADIC,
           SqlFunctionCategory.NUMERIC)
           .withSyntax(SqlSyntax.FUNCTION_ID);
 
diff --git a/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java b/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java
index 6b510e41417..35373d7b508 100644
--- a/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java
+++ b/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java
@@ -93,6 +93,27 @@ public static void unparseSparkArrayAndMap(SqlWriter writer,
     writer.endList(frame);
   }
 
+  /**
+   * Unparses PI function without parentheses.
+   *
+   * <p>For example :
+   *
+   * <blockquote><pre>
+   * SELECT PI &rarr; SELECT PI()
+   * </pre></blockquote>
+   *
+   * @param writer writer
+   * @param call the call
+   */
+  public static void unparsePI(
+      SqlWriter writer,
+      SqlCall call,
+      int leftPrec,
+      int rightPrec) {
+    final SqlWriter.Frame trimFrame = writer.startFunCall(call.getKind().name());
+    writer.endFunCall(trimFrame);
+  }
+
   /**
    * Unparses TRIM function with value as space.
    *
diff --git a/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java b/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
index d855bb96c38..5e188c19f86 100644
--- a/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
+++ b/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
@@ -357,6 +357,29 @@ private static String toSql(RelNode root, SqlDialect dialect,
         .withStarRocks().ok(expectedStarRocks);
   }
 
+  /** Test case for <a href="https://issues.apache.org/jira/browse/CALCITE-6566">[CALCITE-6566]</a>
+   * JDBC adapter should generate PI function with parentheses
+   * When unparse PI function without parentheses. */
+  @Test void testPiFunction() {
+    String query = "select PI";
+    final String expected = "SELECT PI AS \"PI\"\nFROM (VALUES (0)) AS \"t\" (\"ZERO\")";
+    final String expectedHive = "SELECT PI() `PI`";
+    final String expectedSpark = "SELECT PI() `PI`\nFROM (VALUES (0)) `t` (`ZERO`)";
+    final String expectedMssql = "SELECT PI() AS [PI]\nFROM (VALUES (0)) AS [t] ([ZERO])";
+    final String expectedMysql = "SELECT PI() AS `PI`";
+    final String expectedClickHouse = "SELECT PI() AS `PI`";
+    final String expectedPresto = "SELECT PI() AS \"PI\"\nFROM (VALUES (0)) AS \"t\" (\"ZERO\")";
+    final String expectedOracle = "SELECT PI \"PI\"\nFROM \"DUAL\"";
+    sql(query).ok(expected)
+        .withHive().ok(expectedHive)
+        .withSpark().ok(expectedSpark)
+        .withMssql().ok(expectedMssql)
+        .withMysql().ok(expectedMysql)
+        .withClickHouse().ok(expectedClickHouse)
+        .withPresto().ok(expectedPresto)
+        .withOracle().ok(expectedOracle);
+  }
+
   @Test void testPivotToSqlFromProductTable() {
     String query = "select * from (\n"
         + "  select \"shelf_width\", \"net_weight\", \"product_id\"\n"

From ae79ae66af0549b1bdfd635c16ff3d21ebae0ef5 Mon Sep 17 00:00:00 2001
From: nobigo <nobigogle@gmail.com>
Date: Thu, 12 Sep 2024 06:09:08 +0800
Subject: [PATCH 2/5] [CALCITE-6566] Code Review

---
 .../org/apache/calcite/sql/SqlDialect.java    |  4 ++++
 .../sql/dialect/CalciteSqlDialect.java        | 13 ++++++++++++
 .../sql/dialect/ClickHouseSqlDialect.java     |  4 ----
 .../calcite/sql/dialect/HiveSqlDialect.java   |  3 ---
 .../calcite/sql/dialect/MssqlSqlDialect.java  |  5 +----
 .../calcite/sql/dialect/MysqlSqlDialect.java  |  7 +++----
 .../calcite/sql/dialect/OracleSqlDialect.java |  4 +++-
 .../sql/dialect/PostgresqlSqlDialect.java     |  4 ----
 .../calcite/sql/dialect/PrestoSqlDialect.java |  3 ---
 .../calcite/sql/dialect/SparkSqlDialect.java  |  4 ----
 .../calcite/util/RelToSqlConverterUtil.java   |  6 ++----
 .../rel/rel2sql/RelToSqlConverterTest.java    | 21 ++++++++++++-------
 12 files changed, 39 insertions(+), 39 deletions(-)

diff --git a/core/src/main/java/org/apache/calcite/sql/SqlDialect.java b/core/src/main/java/org/apache/calcite/sql/SqlDialect.java
index 9ebc4c383c4..c84de56513c 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlDialect.java
@@ -40,6 +40,7 @@
 import org.apache.calcite.sql.type.SqlTypeUtil;
 import org.apache.calcite.sql.validate.SqlConformance;
 import org.apache.calcite.sql.validate.SqlConformanceEnum;
+import org.apache.calcite.util.RelToSqlConverterUtil;
 import org.apache.calcite.util.format.FormatModel;
 import org.apache.calcite.util.format.FormatModels;
 
@@ -446,6 +447,9 @@ public void unparseCall(SqlWriter writer, SqlCall call, int leftPrec,
       int rightPrec) {
     SqlOperator operator = call.getOperator();
     switch (call.getKind()) {
+    case PI:
+      RelToSqlConverterUtil.unparsePiFunction(writer, call);
+      break;
     case ROW:
       // Remove the ROW keyword if the dialect does not allow that.
       if (!getConformance().allowExplicitRowValueConstructor()) {
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/CalciteSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/CalciteSqlDialect.java
index f9c381c9217..a0dc044519a 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/CalciteSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/CalciteSqlDialect.java
@@ -16,7 +16,9 @@
  */
 package org.apache.calcite.sql.dialect;
 
+import org.apache.calcite.sql.SqlCall;
 import org.apache.calcite.sql.SqlDialect;
+import org.apache.calcite.sql.SqlWriter;
 
 /**
  * A <code>SqlDialect</code> implementation that produces SQL that can be parsed
@@ -39,4 +41,15 @@ public class CalciteSqlDialect extends SqlDialect {
   public CalciteSqlDialect(Context context) {
     super(context);
   }
+
+  @Override public void unparseCall(SqlWriter writer, SqlCall call,
+      int leftPrec, int rightPrec) {
+    switch (call.getKind()) {
+    case PI:
+      call.getOperator().unparse(writer, call, leftPrec, rightPrec);
+      break;
+    default:
+      super.unparseCall(writer, call, leftPrec, rightPrec);
+    }
+  }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/ClickHouseSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/ClickHouseSqlDialect.java
index 5e43267ccb8..9fc3618924b 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/ClickHouseSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/ClickHouseSqlDialect.java
@@ -33,7 +33,6 @@
 import org.apache.calcite.sql.parser.SqlParserPos;
 import org.apache.calcite.sql.type.BasicSqlType;
 import org.apache.calcite.sql.type.SqlTypeName;
-import org.apache.calcite.util.RelToSqlConverterUtil;
 
 import org.checkerframework.checker.nullness.qual.Nullable;
 
@@ -204,9 +203,6 @@ private static SqlDataTypeSpec createSqlDataTypeSpecByName(String typeAlias,
       call.operand(1).unparse(writer, 0, 0);
       writer.endList(frame);
       break;
-    case PI:
-      RelToSqlConverterUtil.unparsePI(writer, call, leftPrec, rightPrec);
-      break;
     default:
       super.unparseCall(writer, call, leftPrec, rightPrec);
     }
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/HiveSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/HiveSqlDialect.java
index ac1bbcadf60..bf40da483e7 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/HiveSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/HiveSqlDialect.java
@@ -109,9 +109,6 @@ public HiveSqlDialect(Context context) {
     case TRIM:
       RelToSqlConverterUtil.unparseHiveTrim(writer, call, leftPrec, rightPrec);
       break;
-    case PI:
-      RelToSqlConverterUtil.unparsePI(writer, call, leftPrec, rightPrec);
-      break;
     default:
       super.unparseCall(writer, call, leftPrec, rightPrec);
     }
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/MssqlSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/MssqlSqlDialect.java
index c7ebb668eb3..6f32a33a4a9 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/MssqlSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/MssqlSqlDialect.java
@@ -40,7 +40,6 @@
 import org.apache.calcite.sql.type.OperandTypes;
 import org.apache.calcite.sql.type.ReturnTypes;
 import org.apache.calcite.sql.type.SqlTypeName;
-import org.apache.calcite.util.RelToSqlConverterUtil;
 
 import org.checkerframework.checker.nullness.qual.Nullable;
 
@@ -173,9 +172,7 @@ public MssqlSqlDialect(Context context) {
         }
         unparseFloor(writer, call);
         break;
-      case PI:
-        RelToSqlConverterUtil.unparsePI(writer, call, leftPrec, rightPrec);
-        break;
+
       default:
         super.unparseCall(writer, call, leftPrec, rightPrec);
       }
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/MysqlSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/MysqlSqlDialect.java
index 1aa27d8993b..fc2a7a1b054 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/MysqlSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/MysqlSqlDialect.java
@@ -48,7 +48,6 @@
 import org.apache.calcite.sql.type.OperandTypes;
 import org.apache.calcite.sql.type.ReturnTypes;
 import org.apache.calcite.sql.type.SqlTypeName;
-import org.apache.calcite.util.RelToSqlConverterUtil;
 
 import com.google.common.collect.ImmutableList;
 
@@ -243,6 +242,7 @@ public MysqlSqlDialect(Context context) {
 
       unparseFloor(writer, call);
       break;
+
     case WITHIN_GROUP:
       final List<SqlNode> operands = call.getOperandList();
       if (operands.size() <= 0 || operands.get(0).getKind() != SqlKind.LISTAGG) {
@@ -252,12 +252,11 @@ public MysqlSqlDialect(Context context) {
       unparseListAggCall(writer, (SqlCall) operands.get(0),
           operands.size() == 2 ? operands.get(1) : null, leftPrec, rightPrec);
       break;
+
     case LISTAGG:
       unparseListAggCall(writer, call, null, leftPrec, rightPrec);
       break;
-    case PI:
-      RelToSqlConverterUtil.unparsePI(writer, call, leftPrec, rightPrec);
-      break;
+
     default:
       super.unparseCall(writer, call, leftPrec, rightPrec);
     }
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/OracleSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/OracleSqlDialect.java
index 75ce64286b5..88720379951 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/OracleSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/OracleSqlDialect.java
@@ -204,7 +204,9 @@ public OracleSqlDialect(Context context) {
                 timeUnitNode.getParserPosition());
         SqlFloorFunction.unparseDatetimeFunction(writer, call2, "TRUNC", true);
         break;
-
+      case PI:
+        call.getOperator().unparse(writer, call, leftPrec, rightPrec);
+        break;
       default:
         super.unparseCall(writer, call, leftPrec, rightPrec);
       }
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/PostgresqlSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/PostgresqlSqlDialect.java
index c2eba8aac98..627b3c79a41 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/PostgresqlSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/PostgresqlSqlDialect.java
@@ -38,7 +38,6 @@
 import org.apache.calcite.sql.fun.SqlStdOperatorTable;
 import org.apache.calcite.sql.parser.SqlParserPos;
 import org.apache.calcite.sql.type.SqlTypeName;
-import org.apache.calcite.util.RelToSqlConverterUtil;
 
 import com.google.common.collect.ImmutableList;
 
@@ -178,9 +177,6 @@ public PostgresqlSqlDialect(Context context) {
               timeUnitNode.getParserPosition());
       SqlFloorFunction.unparseDatetimeFunction(writer, call2, "DATE_TRUNC", false);
       break;
-    case PI:
-      RelToSqlConverterUtil.unparsePI(writer, call, leftPrec, rightPrec);
-      break;
     default:
       super.unparseCall(writer, call, leftPrec, rightPrec);
     }
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/PrestoSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/PrestoSqlDialect.java
index 961870cb464..4b6c7c3292d 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/PrestoSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/PrestoSqlDialect.java
@@ -145,9 +145,6 @@ private static void unparseUsingLimit(SqlWriter writer, @Nullable SqlNode offset
       case MAP_VALUE_CONSTRUCTOR:
         unparseMapValue(writer, call, leftPrec, rightPrec);
         break;
-      case PI:
-        RelToSqlConverterUtil.unparsePI(writer, call, leftPrec, rightPrec);
-        break;
       default:
         // Current impl is same with Postgresql.
         PostgresqlSqlDialect.DEFAULT.unparseCall(writer, call, leftPrec, rightPrec);
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/SparkSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/SparkSqlDialect.java
index c8e0254b069..c2daf0ab677 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/SparkSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/SparkSqlDialect.java
@@ -34,7 +34,6 @@
 import org.apache.calcite.sql.parser.SqlParserPos;
 import org.apache.calcite.sql.type.BasicSqlType;
 import org.apache.calcite.sql.type.SqlTypeName;
-import org.apache.calcite.util.RelToSqlConverterUtil;
 
 import org.checkerframework.checker.nullness.qual.Nullable;
 
@@ -140,9 +139,6 @@ public SparkSqlDialect(SqlDialect.Context context) {
     case POSITION:
       SqlUtil.unparseFunctionSyntax(SqlStdOperatorTable.POSITION, writer, call, false);
       break;
-    case PI:
-      RelToSqlConverterUtil.unparsePI(writer, call, leftPrec, rightPrec);
-      break;
     default:
       super.unparseCall(writer, call, leftPrec, rightPrec);
     }
diff --git a/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java b/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java
index 35373d7b508..69a084561ee 100644
--- a/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java
+++ b/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java
@@ -105,11 +105,9 @@ public static void unparseSparkArrayAndMap(SqlWriter writer,
    * @param writer writer
    * @param call the call
    */
-  public static void unparsePI(
+  public static void unparsePiFunction(
       SqlWriter writer,
-      SqlCall call,
-      int leftPrec,
-      int rightPrec) {
+      SqlCall call) {
     final SqlWriter.Frame trimFrame = writer.startFunCall(call.getKind().name());
     writer.endFunCall(trimFrame);
   }
diff --git a/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java b/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
index 5e188c19f86..abbde238d4a 100644
--- a/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
+++ b/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
@@ -358,19 +358,24 @@ private static String toSql(RelNode root, SqlDialect dialect,
   }
 
   /** Test case for <a href="https://issues.apache.org/jira/browse/CALCITE-6566">[CALCITE-6566]</a>
-   * JDBC adapter should generate PI function with parentheses
-   * When unparse PI function without parentheses. */
+   * JDBC adapter should generate PI function with parentheses in most dialects. */
   @Test void testPiFunction() {
     String query = "select PI";
-    final String expected = "SELECT PI AS \"PI\"\nFROM (VALUES (0)) AS \"t\" (\"ZERO\")";
+    final String expected = "SELECT PI AS \"PI\"\n"
+        + "FROM (VALUES (0)) AS \"t\" (\"ZERO\")";
     final String expectedHive = "SELECT PI() `PI`";
-    final String expectedSpark = "SELECT PI() `PI`\nFROM (VALUES (0)) `t` (`ZERO`)";
-    final String expectedMssql = "SELECT PI() AS [PI]\nFROM (VALUES (0)) AS [t] ([ZERO])";
+    final String expectedSpark = "SELECT PI() `PI`\n"
+        + "FROM (VALUES (0)) `t` (`ZERO`)";
+    final String expectedMssql = "SELECT PI() AS [PI]\n"
+        + "FROM (VALUES (0)) AS [t] ([ZERO])";
     final String expectedMysql = "SELECT PI() AS `PI`";
     final String expectedClickHouse = "SELECT PI() AS `PI`";
-    final String expectedPresto = "SELECT PI() AS \"PI\"\nFROM (VALUES (0)) AS \"t\" (\"ZERO\")";
-    final String expectedOracle = "SELECT PI \"PI\"\nFROM \"DUAL\"";
-    sql(query).ok(expected)
+    final String expectedPresto = "SELECT PI() AS \"PI\"\n"
+        + "FROM (VALUES (0)) AS \"t\" (\"ZERO\")";
+    final String expectedOracle = "SELECT PI \"PI\"\n"
+        + "FROM \"DUAL\"";
+    sql(query)
+        .ok(expected)
         .withHive().ok(expectedHive)
         .withSpark().ok(expectedSpark)
         .withMssql().ok(expectedMssql)

From 3f9c5f0ecb94d257e637fcad7e4d94a102561022 Mon Sep 17 00:00:00 2001
From: nobigo <nobigogle@gmail.com>
Date: Thu, 19 Sep 2024 06:49:03 +0800
Subject: [PATCH 3/5] [CALCITE-6566] Support PI() replace PI

---
 .../org/apache/calcite/sql/SqlDialect.java    |  4 --
 .../sql/dialect/CalciteSqlDialect.java        | 13 -------
 .../calcite/sql/dialect/OracleSqlDialect.java |  2 +-
 .../calcite/sql/fun/SqlStdOperatorTable.java  |  4 +-
 .../calcite/util/RelToSqlConverterUtil.java   | 19 ----------
 .../rel/rel2sql/RelToSqlConverterTest.java    | 37 ++++++++++++++-----
 6 files changed, 30 insertions(+), 49 deletions(-)

diff --git a/core/src/main/java/org/apache/calcite/sql/SqlDialect.java b/core/src/main/java/org/apache/calcite/sql/SqlDialect.java
index c84de56513c..9ebc4c383c4 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlDialect.java
@@ -40,7 +40,6 @@
 import org.apache.calcite.sql.type.SqlTypeUtil;
 import org.apache.calcite.sql.validate.SqlConformance;
 import org.apache.calcite.sql.validate.SqlConformanceEnum;
-import org.apache.calcite.util.RelToSqlConverterUtil;
 import org.apache.calcite.util.format.FormatModel;
 import org.apache.calcite.util.format.FormatModels;
 
@@ -447,9 +446,6 @@ public void unparseCall(SqlWriter writer, SqlCall call, int leftPrec,
       int rightPrec) {
     SqlOperator operator = call.getOperator();
     switch (call.getKind()) {
-    case PI:
-      RelToSqlConverterUtil.unparsePiFunction(writer, call);
-      break;
     case ROW:
       // Remove the ROW keyword if the dialect does not allow that.
       if (!getConformance().allowExplicitRowValueConstructor()) {
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/CalciteSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/CalciteSqlDialect.java
index a0dc044519a..f9c381c9217 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/CalciteSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/CalciteSqlDialect.java
@@ -16,9 +16,7 @@
  */
 package org.apache.calcite.sql.dialect;
 
-import org.apache.calcite.sql.SqlCall;
 import org.apache.calcite.sql.SqlDialect;
-import org.apache.calcite.sql.SqlWriter;
 
 /**
  * A <code>SqlDialect</code> implementation that produces SQL that can be parsed
@@ -41,15 +39,4 @@ public class CalciteSqlDialect extends SqlDialect {
   public CalciteSqlDialect(Context context) {
     super(context);
   }
-
-  @Override public void unparseCall(SqlWriter writer, SqlCall call,
-      int leftPrec, int rightPrec) {
-    switch (call.getKind()) {
-    case PI:
-      call.getOperator().unparse(writer, call, leftPrec, rightPrec);
-      break;
-    default:
-      super.unparseCall(writer, call, leftPrec, rightPrec);
-    }
-  }
 }
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/OracleSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/OracleSqlDialect.java
index 88720379951..231c560a0dc 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/OracleSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/OracleSqlDialect.java
@@ -205,7 +205,7 @@ public OracleSqlDialect(Context context) {
         SqlFloorFunction.unparseDatetimeFunction(writer, call2, "TRUNC", true);
         break;
       case PI:
-        call.getOperator().unparse(writer, call, leftPrec, rightPrec);
+        writer.sep(call.getOperator().getName());
         break;
       default:
         super.unparseCall(writer, call, leftPrec, rightPrec);
diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlStdOperatorTable.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlStdOperatorTable.java
index 0ab0a240b16..d0b694165ba 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlStdOperatorTable.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlStdOperatorTable.java
@@ -50,7 +50,6 @@
 import org.apache.calcite.sql.SqlSetOperator;
 import org.apache.calcite.sql.SqlSetSemanticsTableOperator;
 import org.apache.calcite.sql.SqlSpecialOperator;
-import org.apache.calcite.sql.SqlSyntax;
 import org.apache.calcite.sql.SqlTumbleTableFunction;
 import org.apache.calcite.sql.SqlUnnestOperator;
 import org.apache.calcite.sql.SqlUtil;
@@ -1816,8 +1815,7 @@ public class SqlStdOperatorTable extends ReflectiveSqlOperatorTable {
   /** The {@code PI} function. */
   public static final SqlFunction PI =
       SqlBasicFunction.create(SqlKind.PI, ReturnTypes.DOUBLE, OperandTypes.NILADIC,
-          SqlFunctionCategory.NUMERIC)
-          .withSyntax(SqlSyntax.FUNCTION_ID);
+          SqlFunctionCategory.NUMERIC);
 
   /** {@code FIRST} function to be used within {@code MATCH_RECOGNIZE}. */
   public static final SqlFunction FIRST =
diff --git a/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java b/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java
index 69a084561ee..6b510e41417 100644
--- a/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java
+++ b/core/src/main/java/org/apache/calcite/util/RelToSqlConverterUtil.java
@@ -93,25 +93,6 @@ public static void unparseSparkArrayAndMap(SqlWriter writer,
     writer.endList(frame);
   }
 
-  /**
-   * Unparses PI function without parentheses.
-   *
-   * <p>For example :
-   *
-   * <blockquote><pre>
-   * SELECT PI &rarr; SELECT PI()
-   * </pre></blockquote>
-   *
-   * @param writer writer
-   * @param call the call
-   */
-  public static void unparsePiFunction(
-      SqlWriter writer,
-      SqlCall call) {
-    final SqlWriter.Frame trimFrame = writer.startFunCall(call.getKind().name());
-    writer.endFunCall(trimFrame);
-  }
-
   /**
    * Unparses TRIM function with value as space.
    *
diff --git a/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java b/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
index abbde238d4a..9dfddb0ad11 100644
--- a/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
+++ b/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
@@ -360,19 +360,19 @@ private static String toSql(RelNode root, SqlDialect dialect,
   /** Test case for <a href="https://issues.apache.org/jira/browse/CALCITE-6566">[CALCITE-6566]</a>
    * JDBC adapter should generate PI function with parentheses in most dialects. */
   @Test void testPiFunction() {
-    String query = "select PI";
-    final String expected = "SELECT PI AS \"PI\"\n"
+    String query = "select PI()";
+    final String expected = "SELECT PI()\n"
         + "FROM (VALUES (0)) AS \"t\" (\"ZERO\")";
-    final String expectedHive = "SELECT PI() `PI`";
-    final String expectedSpark = "SELECT PI() `PI`\n"
+    final String expectedHive = "SELECT PI()";
+    final String expectedSpark = "SELECT PI()\n"
         + "FROM (VALUES (0)) `t` (`ZERO`)";
-    final String expectedMssql = "SELECT PI() AS [PI]\n"
+    final String expectedMssql = "SELECT PI()\n"
         + "FROM (VALUES (0)) AS [t] ([ZERO])";
-    final String expectedMysql = "SELECT PI() AS `PI`";
-    final String expectedClickHouse = "SELECT PI() AS `PI`";
-    final String expectedPresto = "SELECT PI() AS \"PI\"\n"
+    final String expectedMysql = "SELECT PI()";
+    final String expectedClickHouse = "SELECT PI()";
+    final String expectedPresto = "SELECT PI()\n"
         + "FROM (VALUES (0)) AS \"t\" (\"ZERO\")";
-    final String expectedOracle = "SELECT PI \"PI\"\n"
+    final String expectedOracle = "SELECT PI\n"
         + "FROM \"DUAL\"";
     sql(query)
         .ok(expected)
@@ -385,6 +385,25 @@ private static String toSql(RelNode root, SqlDialect dialect,
         .withOracle().ok(expectedOracle);
   }
 
+  @Test void testNiladicCurrentDateFunction() {
+    String query = "select CURRENT_DATE";
+    final String expected = "SELECT CURRENT_DATE AS \"CURRENT_DATE\"\n"
+        + "FROM (VALUES (0)) AS \"t\" (\"ZERO\")";
+    final String expectedPostgresql = "SELECT CURRENT_DATE AS \"CURRENT_DATE\"\n"
+        + "FROM (VALUES (0)) AS \"t\" (\"ZERO\")";
+    final String expectedSpark = "SELECT CURRENT_DATE `CURRENT_DATE`\n"
+        + "FROM (VALUES (0)) `t` (`ZERO`)";
+    final String expectedMysql = "SELECT CURRENT_DATE AS `CURRENT_DATE`";
+    final String expectedOracle = "SELECT CURRENT_DATE \"CURRENT_DATE\"\n"
+        + "FROM \"DUAL\"";
+    sql(query)
+        .ok(expected)
+        .withPostgresql().ok(expectedPostgresql)
+        .withSpark().ok(expectedSpark)
+        .withMysql().ok(expectedMysql)
+        .withOracle().ok(expectedOracle);
+  }
+
   @Test void testPivotToSqlFromProductTable() {
     String query = "select * from (\n"
         + "  select \"shelf_width\", \"net_weight\", \"product_id\"\n"

From 08cb0850193230beae5e3a337bd27d6679274276 Mon Sep 17 00:00:00 2001
From: nobigo <nobigogle@gmail.com>
Date: Thu, 19 Sep 2024 07:17:20 +0800
Subject: [PATCH 4/5] [CALCITE-6566] Make test pass

---
 babel/src/test/resources/sql/redshift.iq | 12 ++++++------
 core/src/test/resources/sql/misc.iq      |  2 +-
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/babel/src/test/resources/sql/redshift.iq b/babel/src/test/resources/sql/redshift.iq
index d5d9f255f3a..76687288c76 100755
--- a/babel/src/test/resources/sql/redshift.iq
+++ b/babel/src/test/resources/sql/redshift.iq
@@ -1476,7 +1476,7 @@ EXPR$0
 2
 !ok
 
-select -abs(-pi);
+select -abs(-pi());
 EXPR$0
 -3.141592653589793
 !ok
@@ -1522,7 +1522,7 @@ EXPR$0
 -10
 !ok
 
-select ceil(pi);
+select ceil(pi());
 EXPR$0
 4.0
 !ok
@@ -1546,7 +1546,7 @@ EXPR$0
 !ok
 
 # DEGREES
-select degrees(pi);
+select degrees(pi());
 EXPR$0
 180.0
 !ok
@@ -1629,17 +1629,17 @@ SELECT "RANDOM"()
 !explain-validated-on calcite
 
 # ROUND
-select round(pi);
+select round(pi());
 EXPR$0
 3.0
 !ok
 
-select round(pi, 2);
+select round(pi(), 2);
 EXPR$0
 3.14
 !ok
 
-select round(-pi, 2);
+select round(-pi(), 2);
 EXPR$0
 -3.14
 !ok
diff --git a/core/src/test/resources/sql/misc.iq b/core/src/test/resources/sql/misc.iq
index 2d61e279507..478075e035c 100644
--- a/core/src/test/resources/sql/misc.iq
+++ b/core/src/test/resources/sql/misc.iq
@@ -1815,7 +1815,7 @@ from (values 1, 2, 3, 4, 5) as t(i);
 !ok
 
 # PI function
-values pi;
+values pi();
 +-------------------+
 | PI                |
 +-------------------+

From bdeaae86c535364d3e78a6faaff6e4d9e258a051 Mon Sep 17 00:00:00 2001
From: nobigo <nobigogle@gmail.com>
Date: Thu, 19 Sep 2024 07:23:49 +0800
Subject: [PATCH 5/5] [CALCITE-6566] Make test pass

---
 core/src/test/resources/sql/misc.iq | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/core/src/test/resources/sql/misc.iq b/core/src/test/resources/sql/misc.iq
index 478075e035c..1dd8e18be9e 100644
--- a/core/src/test/resources/sql/misc.iq
+++ b/core/src/test/resources/sql/misc.iq
@@ -1817,7 +1817,7 @@ from (values 1, 2, 3, 4, 5) as t(i);
 # PI function
 values pi();
 +-------------------+
-| PI                |
+| EXPR$0            |
 +-------------------+
 | 3.141592653589793 |
 +-------------------+
@@ -1826,7 +1826,7 @@ values pi();
 !ok
 
 # DEGREES function
-values (degrees(pi), degrees(-pi / 2));
+values (degrees(pi()), degrees(-pi() / 2));
 +--------+--------+
 | EXPR$0 | EXPR$1 |
 +--------+--------+