The position expression, like "1" in "order by 1" was parsed ito `*ast.ValueExpr` in parser, replaced to position expression by resolver, But flag setter sets flag before resolving process, so position flag is not set.
The position expression, like "1" in "order by 1" was parsed ito `*ast.ValueExpr` in parser, replaced to position expression by resolver, But flag setter sets flag before resolving process, so position flag is not set.