Re: How to get columnName as `COUNT(*)` , not `EXPR$0`

[XING JIN]

You can check the below doc of SqlValidatorUtil#getAlias for explanation:

  /**
   * Derives an alias for a node, and invents a mangled identifier if it
   * cannot.
   *
   * <p>Examples:
   *
   * <ul>
   * <li>Alias: "1 + 2 as foo" yields "foo"
   * <li>Identifier: "foo.bar.baz" yields "baz"
   * <li>Anything else yields "expr$<i>ordinal</i>"
   * </ul>
   *
   * @return An alias, if one can be derived; or a synthetic alias
   * "expr$<i>ordinal</i>" if ordinal &lt; 0; otherwise null
   */
  public static String getAlias(SqlNode node, int ordinal)

But from my experience, you'd better not rely on above logic heavily. If
you really care about the output name, just give it an alias explicitly.

Juan Pan <panj...@apache.org> 于2019年9月29日周日 下午1:27写道：

> That means Calcite can only return real columnName or columnLabel from
> simple column or alias. And any aggregate function, or calculate expression
> without alias, parsing expression, i.e, `EXPR$0` will be returned?
>
>
>  Juan Pan
>
>
> panj...@apache.org
> Juan Pan(Trista), Apache ShardingSphere
>
>
> On 09/29/2019 13:16，XING JIN<jinxing.co...@gmail.com> wrote：
> If no column name given explicitly, e.g. by alias or simple identifier,
> Calcite will derive one but not from the aggregate function.
>
> Juan Pan <panj...@apache.org> 于2019年9月29日周日 下午1:12写道：
>
> Thank for your reply. It is a indirect way to get columnName.
>
>
> Calcite can not return the real columnName from SQL, is it right?
>
>
> Juan Pan
>
>
> panj...@apache.org
> Juan Pan(Trista), Apache ShardingSphere
>
>
> On 09/29/2019 12:21，XING JIN<jinxing.co...@gmail.com> wrote：
> You can try to give an alias for the selected column.
>
> Juan Pan <panj...@apache.org> 于2019年9月29日周日 上午11:39写道：
>
>
>
> Hi everyone,
>
>
> I executed SQL `select count(*) from tb1` through Calcite and
> resultSet.getMetaData().getColumnName(i) in my project. But the result is
> `EXPR$0` not `COUNT(*)`.
>
>
> Is there any way to get real columnName?
>
>
> Thanks for your attention.
>
>
> Regard,
> Trista
>
>
>
>
> Juan Pan
>
>
> panj...@apache.org
> Juan Pan(Trista), Apache ShardingSphere
>
>
>
>