MySQL unparser emits CAST(x AS TINYINT), which MySQL rejects #26882

Describe the bug

MySqlDialect overrides int32_cast_dtype and int64_cast_dtype to return SIGNED, but does not override int8_cast_dtype. An Int8 cast therefore unparses with the default TINYINT.

MySQL's CAST does not accept TINYINT as a target type (see the permitted types).

To Reproduce

let unparser = Unparser::new(&MySqlDialect {});
let expr = Expr::Cast(Cast::new(Box::new(col("a")), DataType::Int8));
println!("{}", unparser.expr_to_sql(&expr)?);
// CAST(`a` AS TINYINT)

Expected behavior

CAST(a AS SIGNED), the same as Int32 and Int64 casts.

Additional context

No response

Willingness to contribute

I plan to contribute a fix for this bug independently