Make CONSTRAINT with string and integer in SQL - sql

Question

I am a beginner. I created a query on PostgreSQL. I want to make CONSTRAINT with string and integer. It was successfully running but when I insert the data, it gave me an error
CREATE TABLE customer
(
id_customer char(5) PRIMARY KEY NOT NULL,
CONSTRAINT cek_id_customer CHECK ((left(id_customer,2) in ('CU'))
and substring(id_customer,3) LIKE '%[0-9]%'),
nama_customer varchar(30) NOT NULL,
gender_customer varchar(15) NOT NULL,
CONSTRAINT cek_gender_customer CHECK(gender_customer = 'Male' OR gender_customer = 'Female')
);
INSERT INTO customer
VALUES ('CU001', 'Sayaa', 'Male')
The message
ERROR: new row for relation "customer" violates check constraint "cek_id_customer"
DETAIL: Failing row contains (CU001, Sayaa, Male).
SQL state: 23514

Answer 1

To enforce the matching pattern you want you can use a regular expression matching rule in the constraint, like id_customer ~ '^CU[0-9]*$'.
For example:
CREATE TABLE customer (
id_customer char(5) PRIMARY KEY NOT NULL,
CONSTRAINT cek_id_customer CHECK (id_customer ~ '^CU[0-9]*$'),
nama_customer varchar(30) NOT NULL,
gender_customer varchar(15) NOT NULL,
CONSTRAINT cek_gender_customer CHECK(
gender_customer = 'Male' OR
gender_customer = 'Female'
)
);
INSERT INTO customer (id_customer, nama_customer, gender_customer)
VALUES ('CU001', 'Sayaa', 'Male'); -- succeeds
INSERT INTO customer (id_customer, nama_customer, gender_customer)
VALUES ('CU1X', 'Sayaa', 'Male'); -- fails!
See running example at DB Fiddle.