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

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

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/OracleSqlDialect.java

@@ -204,7 +204,9 @@ public OracleSqlDialect(Context context) {
                 timeUnitNode.getParserPosition());
         SqlFloorFunction.unparseDatetimeFunction(writer, call2, "TRUNC", true);
         break;
-
+      case PI:
+        writer.sep(call.getOperator().getName());
+        break;
       default:
         super.unparseCall(writer, call, leftPrec, rightPrec);
       }

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;
@@ -1815,9 +1814,8 @@ public class SqlStdOperatorTable extends ReflectiveSqlOperatorTable {
 
   /** The {@code PI} function. */
   public static final SqlFunction PI =
-      SqlBasicFunction.create("PI", ReturnTypes.DOUBLE, OperandTypes.NILADIC,
-          SqlFunctionCategory.NUMERIC)
-          .withSyntax(SqlSyntax.FUNCTION_ID);
+      SqlBasicFunction.create(SqlKind.PI, ReturnTypes.DOUBLE, OperandTypes.NILADIC,
+          SqlFunctionCategory.NUMERIC);
 
   /** {@code FIRST} function to be used within {@code MATCH_RECOGNIZE}. */
   public static final SqlFunction FIRST =

core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java

@@ -357,6 +357,53 @@ 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 in most dialects. */
+  @Test void testPiFunction() {
+    String query = "select PI()";
+    final String expected = "SELECT PI()\n"
+        + "FROM (VALUES (0)) AS \"t\" (\"ZERO\")";
+    final String expectedHive = "SELECT PI()";
+    final String expectedSpark = "SELECT PI()\n"
+        + "FROM (VALUES (0)) `t` (`ZERO`)";
+    final String expectedMssql = "SELECT PI()\n"
+        + "FROM (VALUES (0)) AS [t] ([ZERO])";
+    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\n"
+        + "FROM \"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 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"

core/src/test/resources/sql/misc.iq

@@ -1815,9 +1815,9 @@ from (values 1, 2, 3, 4, 5) as t(i);
 !ok
 
 # PI function
-values pi;
+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 |
 +--------+--------+