Add support for Dictionary to AST datatype in unparser

[cetra3]

Which issue does this PR close?

No issue raised, just something we've seen in production

Rationale for this change

Ensures we can convert dictionary & interval types to ast datatypes

What changes are included in this PR?

Adds a small change to support dictionaries

Are these changes tested?

I am actually not too sure how best to test this, might need a bit of guidance here if we wanna add a test

Are there any user-facing changes?

No

[alamb]

Thanks @cetra3

@phillipleblanc do you have any suggestions about where we could test this one?

[alamb]

Thank you @cetra3

Ideally we would write a test for this., but since I couldn't find any existing tests for data types, I don't think it is strictly necessary here

Maybe @phillipleblanc has some idea of how to write such a test

[phillipleblanc]

Thank you @cetra3

Ideally we would write a test for this., but since I couldn't find any existing tests for data types, I don't think it is strictly necessary here

Maybe @phillipleblanc has some idea of how to write such a test

There are tests at the bottom of this file that can be added - see for example this PR I made for supporting Utf8View: #13462

[phillipleblanc]

Let's add a test for this new type, see this example for supporting the Utf8View type:

    #[test]
    fn test_utf8_view_to_sql() -> Result<()> {
        let dialect = CustomDialectBuilder::new()
            .with_utf8_cast_dtype(ast::DataType::Char(None))
            .build();
        let unparser = Unparser::new(&dialect);

        let ast_dtype = unparser.arrow_dtype_to_ast_dtype(&DataType::Utf8View)?;

        assert_eq!(ast_dtype, ast::DataType::Char(None));

        let expr = cast(col("a"), DataType::Utf8View);
        let ast = unparser.expr_to_sql(&expr)?;

        let actual = format!("{}", ast);
        let expected = r#"CAST(a AS CHAR)"#.to_string();

        assert_eq!(actual, expected);

        let expr = col("a").eq(lit(ScalarValue::Utf8View(Some("hello".to_string()))));
        let ast = unparser.expr_to_sql(&expr)?;

        let actual = format!("{}", ast);
        let expected = r#"(a = 'hello')"#.to_string();

        assert_eq!(actual, expected);

        let expr = col("a").is_not_null();

        let ast = unparser.expr_to_sql(&expr)?;
        let actual = format!("{}", ast);
        let expected = r#"a IS NOT NULL"#.to_string();

        assert_eq!(actual, expected);

        let expr = col("a").is_null();

        let ast = unparser.expr_to_sql(&expr)?;
        let actual = format!("{}", ast);
        let expected = r#"a IS NULL"#.to_string();

        assert_eq!(actual, expected);

        Ok(())
    }

[cetra3]

I've added a test for this. Let me know if I need to flesh it out more

[cetra3]

I've added this as well, it seems to be a bit of a trivial conversion so not sure a test is warranted

[alamb]

Thank you @cetra3 and @phillipleblanc

[alamb]

❤️