Document IDENTICAL_OPERATOR_FUNCTION_NAME in StandardFunctions

Author: hqbhoho

core/trino-spi/src/main/java/io/trino/spi/expression/StandardFunctions.java

@@ -52,6 +52,9 @@ private StandardFunctions() {}
     public static final FunctionName LESS_THAN_OR_EQUAL_OPERATOR_FUNCTION_NAME = new FunctionName("$less_than_or_equal");
     public static final FunctionName GREATER_THAN_OPERATOR_FUNCTION_NAME = new FunctionName("$greater_than");
     public static final FunctionName GREATER_THAN_OR_EQUAL_OPERATOR_FUNCTION_NAME = new FunctionName("$greater_than_or_equal");
+    /**
+     * $identical function is equivalent to the SQL operator "IS NOT DISTINCT FROM".
+     */
     public static final FunctionName IDENTICAL_OPERATOR_FUNCTION_NAME = new FunctionName("$identical");
 
     /**