mihaibudiu commented on code in PR #5108:
URL: https://github.com/apache/calcite/pull/5108#discussion_r3791043113
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core/src/main/java/org/apache/calcite/rel/rel2sql/SqlImplementor.java:
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@@ -1608,6 +1630,77 @@ public static SqlNode toSql(@Nullable RexProgram
program, RexLiteral literal) {
}
}
+ /** Converts a {@link RexLiteral} in the context of a {@link RexProgram}
+ * to a {@link SqlNode}, preserving the literal's type.
+ *
+ * <p>The SQL text of a literal does not always imply the literal's type:
+ * {@code 1} parses as INTEGER even if the literal's type is TINYINT, and
+ * {@code NULL} loses its type entirely. This method wraps such literals in
+ * a CAST that makes the type explicit; {@code dialect} supplies the SQL
+ * syntax of the CAST target type. */
+ public static SqlNode toSql(@Nullable RexProgram program, RexLiteral literal,
+ SqlDialect dialect) {
+ switch (literal.getTypeName()) {
+ case ROW:
+ // Cast the fields rather than the ROW call, because few dialects can
+ // parse a cast to a ROW type.
+ //noinspection unchecked
+ final List<RexLiteral> list =
castNonNull(literal.getValueAs(List.class));
+ return SqlStdOperatorTable.ROW.createCall(POS,
+ list.stream().map(e -> toSql(program, e, dialect))
+ .collect(toImmutableList()));
+
+ case SYMBOL:
+ case SARG:
+ return toSql(program, literal);
+
+ default:
+ final SqlNode node = toSql(program, literal);
+ // A result that is not a SqlLiteral is already a CAST; for example
+ // NaN becomes CAST('NaN' AS DOUBLE).
+ return node instanceof SqlLiteral
+ ? castIfTypeAmbiguous((SqlLiteral) node, literal.getType(), dialect)
+ : node;
+ }
+ }
+
+ /** Wraps a literal in a CAST to {@code type} if the type that the
+ * validator would infer for the literal's SQL text differs from
+ * {@code type}. */
+ private static SqlNode castIfTypeAmbiguous(SqlLiteral literal, RelDataType
type,
+ SqlDialect dialect) {
+ switch (type.getSqlTypeName()) {
+ case NULL:
+ case ANY:
+ case UNKNOWN:
+ // No valid SQL syntax for casts to these types
Review Comment:
I would expect the NULL case is reachable, e.g., in a query like `SELECT
NULL`, which is legal.
There are actually about 500+ round-trip tests added: the subclass
`RelToSqlConverterRoundTripTest` runs almost every test from
`RelToSqlConverterTest`. There are several tests that contain a `SELECT NULL`
pattern.
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