What it returns is the defined length of the particular column.
5>
6> CREATE TABLE publishers(
7> pub_id char(4) NOT NULL,
8> pub_name varchar(40) NULL,
9> city varchar(20) NULL,
10> state char(2) NULL,
11> country varchar(30) NULL DEFAULT("USA")
12> )
13> GO
1>
2>
3> insert publishers values("1", "Publisher A", "Vancouver", "MA", "USA")
4> insert publishers values("2", "Publisher B", "Washington", "DC", "USA")
5> insert publishers values("3", "Publisher C", "Berkeley", "CA", "USA")
6> insert publishers values("4", "Publisher D", "New York", "NY", "USA")
7> insert publishers values("5", "Publisher E", "Chicago", "IL", "USA")
8> insert publishers values("6", "Publisher F", "Dallas", "TX", "USA")
9> insert publishers values("7", "Publisher G", "Vancouver", "BC", "Canada")
10> insert publishers values("8", "Publisher H", "Paris", NULL, "France")
11> GO
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
1> SELECT COL_LENGTH("publishers", "pub_id")
2> GO
------
4
(1 rows affected)
1>
2> drop table publishers;
3> GO
1>