MySQL 8.0

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CREATE TABLE addresses ( 
  id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
  line_1 VARCHAR(40),
  line_2 VARCHAR(40),
  line_3 VARCHAR(40),
  postal_code VARCHAR(40)
);
CREATE UNIQUE INDEX unique_address ON addresses (line_1, line_2, line_3, postal_code);

Records: 0  Duplicates: 0  Warnings: 0


INSERT INTO addresses (line_1, line_2, line_3, postal_code)
values ('foo 1', 'foo 2', 'foo 3', 'pc1');
INSERT INTO addresses (line_1, line_2, line_3, postal_code)
values ('blah 1', 'blah 2', 'blah 3', 'pc1');
select *
from addresses
where line_1 = 'foo 1'
and line_2 = 'foo 2'
and line_3 = 'foo 3'
and postal_code = 'pc1';


id
line_1
line_2
line_3
postal_code


1
foo 1
foo 2
foo 3
pc1


INSERT INTO addresses (line_1, line_2, line_3, postal_code)
values ('Foo 1', 'Foo 2', 'FOO 3', 'PC1');

Duplicate entry 'Foo 1-Foo 2-FOO 3-PC1' for key 'addresses.unique_address'