zabetak commented on code in PR #4403:
URL: https://github.com/apache/calcite/pull/4403#discussion_r2125965297
##########
core/src/main/java/org/apache/calcite/sql/fun/SqlInternalOperators.java:
##########
@@ -224,6 +224,40 @@ private SqlInternalOperators() {
public static final SqlAggFunction LITERAL_AGG =
SqlLiteralAggFunction.INSTANCE;
+ /** CAST NOT NULL operator used for cast expression to make it non-nullable
in SqlNode.
+ *
+ * <p>For example:
+ * <pre>{@code COALESCE(a,b)
+ * }</pre>
+ *
+ * <p>is converted to
+ *
+ * <pre>{@code CASE WHEN a is not null THEN a ELSE b
+ * }</pre>
+ * by {@code SqlCoalesceFunction#rewriteCall}.
+ *
+ * <p>When a is nullable and b is non-nullable, the {@code COALESCE(a,b)}
data type will be
+ * non-nullable and {@code CASE WHEN a is not null THEN a ELSE b} data type
will be nullable.
Review Comment:
If CALCITE-3675 is now redundant shouldn't we remove the respective code?
##########
core/src/main/java/org/apache/calcite/sql/fun/SqlInternalOperators.java:
##########
@@ -224,6 +224,40 @@ private SqlInternalOperators() {
public static final SqlAggFunction LITERAL_AGG =
SqlLiteralAggFunction.INSTANCE;
+ /** CAST NOT NULL operator used for cast expression to make it non-nullable
in SqlNode.
+ *
+ * <p>For example:
+ * <pre>{@code COALESCE(a,b)
+ * }</pre>
+ *
+ * <p>is converted to
+ *
+ * <pre>{@code CASE WHEN a is not null THEN a ELSE b
+ * }</pre>
+ * by {@code SqlCoalesceFunction#rewriteCall}.
+ *
+ * <p>When a is nullable and b is non-nullable, the {@code COALESCE(a,b)}
data type will be
+ * non-nullable and {@code CASE WHEN a is not null THEN a ELSE b} data type
will be nullable.
+ * The validator will throw an exception about failing to preserve the data
type.
+ *
+ * <p>Add CAST NOT NULL operator to {@code CASE WHEN a is not null THEN a
ELSE b},
+ * making it becomes
+ * <pre>{@code CASE WHEN a is not null THEN CAST NOT NULL(a) ELSE b}
+ * </pre>
+ *
+ * <p>Then the validator knows this data type is non-nullable.
+ * So we can keep the types consistent before and after conversion.
+ * */
+ public static final SqlOperator CAST_NOT_NULL =
+ new SqlInternalOperator("CAST NOT NULL", SqlKind.CAST_NOT_NULL, 2, true,
+ ReturnTypes.ARG0.andThen(SqlTypeTransforms.TO_NOT_NULLABLE), null,
+ OperandTypes.ANY) {
+ // This is an internal operator, which should not be unparsed to sql.
+ @Override public void unparse(SqlWriter writer, SqlCall call, int
leftPrec, int rightPrec) {
+ call.operand(0).unparse(writer, leftPrec, rightPrec);
+ }
Review Comment:
If we never expect to see this operator in SQL then I guess we don't need to
override the unparse method.
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