[GitHub] [calcite] wojustme commented on a diff in pull request #2812: [CALCITE-5163] MysqlSqlDialect support to unparse LISTAGG aggregate function

[GitBox <gi...@apache.org>]

wojustme commented on code in PR #2812:
URL: https://github.com/apache/calcite/pull/2812#discussion_r880076497


##########
core/src/main/java/org/apache/calcite/sql/dialect/MysqlSqlDialect.java:
##########
@@ -223,11 +229,56 @@ 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) {
+        super.unparseCall(writer, call, leftPrec, rightPrec);
+        return;
+      }
+      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;
+
     default:
       super.unparseCall(writer, call, leftPrec, rightPrec);
     }
   }
 
+  /**
+   * Unparses LISTAGG for MySQL. This call is translated to GROUP_CONCAT.
+   *
+   * @param writer Writer
+   * @param listAggCall Call of LISTAGG
+   * @param orderItemNode Elems of WITHIN_GROUP, NULL means none elem in the WITHIN_GROUP
+   * @param leftPrec Origin leftPrec
+   * @param rightPrec Origin rightPrec
+   */
+  private void unparseListAggCall(SqlWriter writer, SqlCall listAggCall,
+      @Nullable SqlNode orderItemNode, int leftPrec, int rightPrec) {
+    // LISTAGG(DISTINCT c1, ',') WITHIN GROUP (ORDER BY c2, c3)
+    // GROUP_CONCAT(DISTINCT c1 ORDER BY c2, c3 DESC SEPARATOR ',')
+    final List<SqlNode> listAggCallOperands = listAggCall.getOperandList();

Review Comment:
   OK.



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