[CALCITE-6383] The class SameOperandTypeChecker is incorrectly docume…

…nted

Signed-off-by: Mihai Budiu <mbudiu@feldera.com>

core/src/main/java/org/apache/calcite/sql/type/SameOperandTypeChecker.java

@@ -37,7 +37,9 @@
 import static java.util.Objects.requireNonNull;
 
 /**
- * Parameter type-checking strategy where all operand types must be the same.
+ * Parameter type-checking strategy where the type of operand I must
+ * be <b>comparable</b> with the type of operand I-1, for all legal values of I.
+ * See {@link SqlTypeUtil#isComparable} for a definition of "comparable" types.
  */
 public class SameOperandTypeChecker implements SqlSingleOperandTypeChecker {
   //~ Instance fields --------------------------------------------------------

core/src/main/java/org/apache/calcite/sql/type/SqlTypeUtil.java

@@ -1467,6 +1467,8 @@ public static boolean isFlat(RelDataType type) {
   /**
    * Returns whether two types are comparable. They need to be scalar types of
    * the same family, or struct types whose fields are pairwise comparable.
+   * Note that types in the CHARACTER family are comparable with many other types
+   * (see {@link #canConvertStringInCompare}).
    *
    * @param type1 First type
    * @param type2 Second type