kosiew commented on code in PR #20590:
URL: https://github.com/apache/datafusion/pull/20590#discussion_r2924826462
##########
datafusion/sql/src/unparser/dialect.rs:
##########
@@ -248,6 +248,17 @@ pub trait Dialect: Send + Sync {
fn supports_empty_select_list(&self) -> bool {
false
}
+
+ /// Override the default string literal unparsing.
+ ///
+ /// Returns `Some(ast::Expr)` to replace the default single-quoted string,
+ /// or `None` to use the default behavior.
+ ///
+ /// For example, MSSQL requires non-ASCII strings to use national string
+ /// literal syntax (`N'datafusion資料融合'`).
+ fn custom_string_literal_override(&self, _s: &str) -> Option<ast::Expr> {
Review Comment:
Since this only affects scalar UTF8 literal unparsing today, a narrower name
or a helper scoped to scalar string literals may make the API easier to
understand and extend. Perhaps `string_literal_to_sql` – to keep the focus on
literals, not “any scalar”?
##########
datafusion/sql/src/unparser/expr.rs:
##########
@@ -2988,6 +2986,57 @@ mod tests {
Ok(())
}
+ #[test]
+ fn test_mssql_dialect_national_literal() -> Result<()> {
+ struct MsSqlDialect;
+
+ impl Dialect for MsSqlDialect {
+ fn identifier_quote_style(&self, _identifier: &str) ->
Option<char> {
+ Some('[')
+ }
+
+ fn custom_string_literal_override(&self, s: &str) ->
Option<ast::Expr> {
+ if !s.is_ascii() {
+ Some(ast::Expr::value(ast::Value::NationalStringLiteral(
+ s.to_string(),
+ )))
+ } else {
+ None
+ }
+ }
+ }
+
+ let dialect = MsSqlDialect;
+ let unparser = Unparser::new(&dialect);
+
+ let expr =
+ Expr::Literal(ScalarValue::Utf8(Some("national
string".to_string())), None);
Review Comment:
The regression test currently exercises `ScalarValue::Utf8`, but the change
also covers `Utf8View` and `LargeUtf8`.
Adding tests for each would make the coverage line up with the
implementation.
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