[CALCITE-6566] JDBC adapter should generate PI function with parenthe…

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,

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,
 

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);
     }

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);
     }

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);
       }

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);
     }

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);
     }

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);

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);
     }

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);
 

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.
    *

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"