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create table users (id int, middle_name varchar2(100))
ALTER TABLE users
ADD CONSTRAINT check_middle_name CHECK (length(middle_name) > 1)
insert into users (id) values (1)
1 rows affected
insert into users (id, middle_name) values (2, 'a')
ORA-02290: check constraint (FIDDLE_CRMZAZZIXHPTOCAEKCMK.CHECK_MIDDLE_NAME) violated
insert into users (id, middle_name) values (2, 'ab')
1 rows affected