fix: [Postgre] updateBatch() breaks char type data

[kenjis]

Description
Follow-up #8439
From https://forum.codeigniter.com/showthread.php?tid=89336

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[sclubricants]

This looks good.

One other option - though I don' t know that it would be any better would be to change CHARACTER into CHARACTER VARYING in the cast method. The only reason is that it would keep the getFieldType() method more 'pure' in a sense. But I'm not sure this would be any better.

[sclubricants]

You could change to CHARACTER | CHAR TO VARCHAR in the cast() method. This should cover the other DBMS too.

https://onecompiler.com/postgresql/423ynm2e2

CREATE TABLE test_table
(
    id      integer,
    char    char(10),
    varchar varchar(10)
);

INSERT INTO test_table (id, char, varchar) VALUES (1, 'foo', 'foo');
INSERT INTO test_table (id, char, varchar) VALUES (2, 'bar', 'bar');
INSERT INTO test_table (id, char, varchar) VALUES (3, 'baz', 'baz');

UPDATE "test_table"
SET "char"    = CAST(_u."char" AS VARCHAR),
    "varchar" = CAST(_u."varchar" AS CHARACTER VARYING)
FROM (SELECT 'Foo' "char", 1 "id", 'Foo' "varchar"
      UNION ALL
      SELECT 'Bar' "char", 2 "id", 'Bar' "varchar"
      UNION ALL
      SELECT 'Baz' "char", 3 "id", 'Baz' "varchar") _u
WHERE "test_table"."id" = CAST(_u."id" AS INTEGER);

SELECT * FROM test_table;

    private function cast($expression, ?string $type): string
    {
        if (strtoupper($type) === 'CHAR' || strtoupper($type) === 'CHARACTER') {
            $type = 'VARCHAR';
        }

        return ($type === null) ? $expression : 'CAST(' . $expression . ' AS ' . strtoupper($type) . ')';
    }

[kenjis]

@sclubricants Thank you for the review!

If character (or char) lacks a specifier, it is equivalent to character(1).
So on PostgreSQL, character(n) seems to be correct type.
And it does not seem to be pure to change CHAR to VARCHAR, too.

Anyway, the method is only for Postgre, and it will override even if the parent class has the method.
So I think there is no problem. Go with this for now.

[sclubricants]

CHAR = CHARACTER
VARCHAR = CHARACTER VARYING
VARCHAR = CHAR of unspecified length

Anyways, looks good

[sclubricants]

SELECT CAST('STRING' AS VARCHAR) AS TEST;

This runs on postgre but not on mysql