[CALCITE-7246] UNNEST in Spark should convert to EXPLODE/POSEXPLODE

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[CALCITE-7246] UNNEST in Spark should  convert to EXPLODE/POSEXPLODE

Author: xiaochen-zhou

core/src/main/java/org/apache/calcite/sql/dialect/SparkSqlDialect.java

@@ -30,6 +30,7 @@
 import org.apache.calcite.sql.SqlLiteral;
 import org.apache.calcite.sql.SqlNode;
 import org.apache.calcite.sql.SqlNodeList;
+import org.apache.calcite.sql.SqlUnnestOperator;
 import org.apache.calcite.sql.SqlUtil;
 import org.apache.calcite.sql.SqlWriter;
 import org.apache.calcite.sql.fun.SqlCase;
@@ -155,6 +156,20 @@ public SparkSqlDialect(SqlDialect.Context context) {
     case POSITION:
       SqlUtil.unparseFunctionSyntax(SqlStdOperatorTable.POSITION, writer, call, false);
       break;
+    case UNNEST:
+      if (call.getOperator() instanceof SqlUnnestOperator
+          && ((SqlUnnestOperator) call.getOperator()).withOrdinality) {
+        writer.keyword("POSEXPLODE");
+      } else {
+        writer.keyword("EXPLODE");
+      }
+      final SqlWriter.Frame frame = writer.startList(SqlWriter.FrameTypeEnum.FUN_CALL, "(", ")");
+      for (SqlNode operand : call.getOperandList()) {
+        writer.sep(",");
+        operand.unparse(writer, 0, 0);
+      }
+      writer.endList(frame);
+      break;
     default:
       super.unparseCall(writer, call, leftPrec, rightPrec);
     }

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

@@ -7814,9 +7814,30 @@ private void checkLiteral2(String expression, String expected) {
     final String expectedHsqldb = "SELECT *\n"
         + "FROM UNNEST((SELECT ARRAY[1, 2, 3]\n"
         + "FROM (VALUES (0)) AS t (ZERO))) AS t0 (col_0)";
+    final String expectedSpark = "SELECT *\n"
+        + "FROM EXPLODE((SELECT ARRAY (1, 2, 3)\n"
+        + "FROM (VALUES (0)) `t` (`ZERO`))) `t0` (`col_0`)";
     sql(sql).ok(expected).
         withPostgresql().ok(expectedPostgresql).
-        withHsqldb().ok(expectedHsqldb);
+        withHsqldb().ok(expectedHsqldb).
+        withSpark().ok(expectedSpark);
+  }
+
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-7246">[CALCITE-7246]
+   * UNNEST in spark should convert to EXPLODE/POSEXPLODE </a>.
+   */
+  @Test void testUnnestArrayWithOrdinality() {
+    final String query = "SELECT * FROM UNNEST(ARRAY[1,2,3]) WITH ORDINALITY";
+    final String expected = "SELECT *\n"
+        + "FROM UNNEST((SELECT ARRAY[1, 2, 3]\n"
+        + "FROM (VALUES (0)) AS \"t\" (\"ZERO\"))) WITH ORDINALITY AS \"t0\" (\"col_0\", \"ORDINALITY\")";
+    final String expectedSpark = "SELECT *\n"
+        + "FROM POSEXPLODE((SELECT ARRAY (1, 2, 3)\n"
+        + "FROM (VALUES (0)) `t` (`ZERO`))) `t0` (`col_0`, `ORDINALITY`)";
+    sql(query)
+        .ok(expected)
+        .withSpark().ok(expectedSpark);
   }
 
   @Test void testWithinGroup1() {