How do I cast a string to integer and have 0 in case of error in the cast with PostgreSQL?

Question

In PostgreSQL I have a table with a varchar column. The data is supposed to be integers and I need it in integer type in a query. Some values are empty strings. The followin

Answer 1

The following function does

• use a default value (error_result) for not castable results e.g abc or 999999999999999999999999999999999999999999
• keeps null as null
• trims away spaces and other whitespace in input
• values casted as valid bigints are compared against lower_bound to e.g enforce positive values only

CREATE OR REPLACE FUNCTION cast_to_bigint(text) 
RETURNS BIGINT AS $$
DECLARE big_int_value BIGINT DEFAULT NULL;
DECLARE error_result  BIGINT DEFAULT -1;
DECLARE lower_bound   BIGINT DEFAULT 0;
BEGIN
    BEGIN
        big_int_value := CASE WHEN $1 IS NOT NULL THEN GREATEST(TRIM($1)::BIGINT, lower_bound) END;
    EXCEPTION WHEN OTHERS THEN
        big_int_value := error_result;
    END;
RETURN big_int_value;
END;

Answer 2

This might be somewhat of a hack, but it got the job done in our case:

(0 || myfield)::integer

Explanation (Tested on Postgres 8.4):

The above mentioned expression yields NULL for NULL-values in myfield and 0 for empty strings (This exact behaviour may or may not fit your use case).

SELECT id, (0 || values)::integer from test_table ORDER BY id

Test data:

CREATE TABLE test_table
(
  id integer NOT NULL,
  description character varying,
  "values" character varying,
  CONSTRAINT id PRIMARY KEY (id)
)

-- Insert Test Data
INSERT INTO test_table VALUES (1, 'null', NULL);
INSERT INTO test_table VALUES (2, 'empty string', '');
INSERT INTO test_table VALUES (3, 'one', '1');

The query will yield the following result:

 ---------------------
 |1|null        |NULL|
 |2|empty string|0   |
 |3|one         |1   |
 ---------------------

Whereas select only values::integer will result in an error message.

Hope this helps.

Answer 3

CREATE OR REPLACE FUNCTION parse_int(s TEXT) RETURNS INT AS $$
BEGIN
  RETURN regexp_replace(('0' || s), '[^\d]', '', 'g')::INT;
END;
$$ LANGUAGE plpgsql;

This function will always return 0 if there are no digits in the input string.

SELECT parse_int('test12_3test');

will return 123

Answer 4

You could also create your own conversion function, inside which you can use exception blocks:

CREATE OR REPLACE FUNCTION convert_to_integer(v_input text)
RETURNS INTEGER AS $$
DECLARE v_int_value INTEGER DEFAULT NULL;
BEGIN
    BEGIN
        v_int_value := v_input::INTEGER;
    EXCEPTION WHEN OTHERS THEN
        RAISE NOTICE 'Invalid integer value: "%".  Returning NULL.', v_input;
        RETURN NULL;
    END;
RETURN v_int_value;
END;
$$ LANGUAGE plpgsql;

Testing:

=# select convert_to_integer('1234');
 convert_to_integer 
--------------------
               1234
(1 row)

=# select convert_to_integer('');
NOTICE:  Invalid integer value: "".  Returning NULL.
 convert_to_integer 
--------------------

(1 row)

=# select convert_to_integer('chicken');
NOTICE:  Invalid integer value: "chicken".  Returning NULL.
 convert_to_integer 
--------------------

(1 row)

Answer 5

SUBSTRING may help for some cases, you can limit the size of the int.

SELECT CAST(SUBSTRING('X12312333333333', '([\d]{1,9})') AS integer);

Answer 6

I also have the same need but that works with JPA 2.0 and Hibernate 5.0.2:

SELECT p FROM MatchProfile p WHERE CONCAT(p.id, '') = :keyword

Works wonders. I think it works with LIKE too.