unique constraint mysql code example

Example 1: mysql set field unique

ALTER TABLE mytbl ADD UNIQUE (columnName);

Example 2: mysql alter table set column unique

ALTER TABLE contacts
ADD CONSTRAINT contacts_unique UNIQUE (reference_number);

Example 3: set column as unique in sql server

ALTER TABLE Persons
ADD UNIQUE (ID);

Example 4: mysql unique two columns

CREATE TABLE IF NOT EXISTS cliente (
	id bigint primary key auto_increment,
    nome varchar(100) not null,
    email varchar(100) not null unique,
    senha varchar(255) not null,
    documento varchar(50) not null unique,
    dataCadastro date not null
) ENGINE = InnoDB DEFAULT CHARSET = utf8mb4;

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