Why doesn't LIKE work with wildcard having % at the beginning?
You might have a problem like this:
CREATE TABLE t1 ( c1 CHAR(5) );
INSERT INTO t1 VALUES ('abcd');
SELECT * FROM t1 WHERE c1 LIKE '%cd';
The above SELECT won't return any rows. The reason is that CHAR columns are always padded with spaces to the full lenght, so column actually contains 'abcd ', with one space at the end. Take a look at FAQ #237 for more details.
To work around this, you should either use VARCHAR, or trim the column using either TRIM or RTRIM functions:
SELECT * FROM t1 WHERE RTRIM(c1) LIKE '%cd';
RTRIM function is a part of IB_UDF UDF library. If you don't have it declared, take a look at FAQ #169 to learn how to enable it.