consider two following sql tables:

CREATE TABLE user $($

user$\_$id int PRIMARY KEY,

first$\_$name varchar$(20)$ DEFAULT NULL,

last$\_$name varchar$(20)$ DEFAULT NULL

$)$

CREATE TABLE omment $($

comment$\_$id int PRIMARY KEY,

rate int DEFAULT NULL,

user$\_$id int NOT NULL,

FOREIGN KEY$($user$\_$id$)$ REFERENCES user$($user$\_$id$)$

$)$

now consider this rule: "The user's first and last name will not be completely displayed, only the first character of the first and last name will be shown."

add a sql constraint that supports this rule.