The PostgreSQL database determines whether it is a numeric and datetime format function

/ *
In the process of writing the GreenPlum function, I encountered the situation of determining whether the string is a number and date format. Based on the relationship between GreenPlum and postgresql, the following two functions were found.
* /

--1. Determine if the string is a number
CREATE OR REPLACE FUNCTION isnumeric (txtStr VARCHAR) RETURNS BOOLEAN
AS
$$
BEGIN
  
RETURN txtStr ~ ‘^ ([0-9] + [.]? [0-9] * | [.] [0-9] +) $’;
  
  
END;
$$
LANGUAGE ‘plpgsql’;

--2. Determine if the incoming string is date format

CREATE OR REPLACE FUNCTION isDate (dateStr VARCHAR) RETURNS BOOLEAN
AS
$$
BEGIN
  
IF (dateStr IS NULL) THEN
      RETURN FALSE;
END IF;
      PERFORM dateStr :: timestamp;
      RETURN TRUE;
EXCEPTION
      WHEN others THEN
      RETURN FALSE;
  
  
END;
$$
LANGUAGE ‘plpgsql’; 

The PostgreSQL database determines whether it is a numeric and datetime format function