[CALCITE-5885] SqlNode#toSqlString() does not honor dialect's supportsCharSet() flag on nested types

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 1.36.0
• Component/s: core
• Labels: pull-request-available
• Assignee: Jiajun Xie
• Reporter: Chris Rice
• Created: 01/Aug/23 22:45
• Updated: 10/Nov/23 11:34
• Resolved: 11/Aug/23 02:09

Description

Say we generate a RelNode corresponding to

SELECT CAST(c AS VARCHAR) FROM t

and we were to "unparse" that rel node back into the Postgres SQL dialect using

var converter = new RelToSqlConverter(PostgresqlSqlDialect.DEFAULT);
SqlImplementor.Result result = converter.visitRoot(rel);
SqlNode sqlNode = result.asStatement();
var sql = sqlNode.toSqlString(PostgresqlSqlDialect.DEFAULT).getSql();

it would generate something like:

SELECT CAST("c" AS VARCHAR) AS "c"
FROM "t"

Note that there is no charset information included in the cast, since the PostgresSqlDialect specifies that it does not support char sets:

  @Override public boolean supportsCharSet() {
    return false;
  }

Given that, we would expect that unparsing

SELECT CAST(c AS VARCHAR ARRAY) FROM t

back into SQL would also generate a type with no charset specified, but it in fact generates

SELECT CAST("c" AS VARCHAR CHARACTER SET "ISO-8859-1" ARRAY) AS "c"
FROM "t"

This seems to come from the way `SqlTypeUtil.convertTypeToSpec()` handles collection types.

Issue Links

• links to: GitHub Pull Request #3349