Generate Unique Key In Mysql

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  1. Creating Unique Key In Mysql
  2. How To Create Unique Key In Mysql

SQL UNIQUE Constraint

MySQL Passwords are used in many PHP / MySQL applications and frameworks, such as Codeigniter. It is the best online free MySQL Password Generator ever built. It takes just a second to generate your MySQL Password. Simply scroll down below, enter your plain text password and click the button to instantly generate the MySQL Password! Jun 09, 2019 Add Unique Key in MySQL Let’s take an example, create a table name person. Here we are storing the data of a person’s details on a website. There are four columns i.e id which is a primary key, Name, Email, Phone. To create a unique constraint. In Object Explorer, right-click the table to which you want to add a unique constraint, and click Design. On the Table Designer menu, click Indexes/Keys. In the Indexes/Keys dialog box, click Add. In the grid under General, click Type and choose Unique Key from the drop-down list box to the right of the property.

  1. In a single DB system, people usually use AUTOINCREMENT columns (e.g. In Mysql) or sequence objects (e.g. In Oracle) that produce unique sequence numbers. These won’t work in a multi-DB environment where different DBs might generate same primary key values that would conflict with each other when new records are synced from one DB to another.
  2. Each multiple field KEY is only allowed to spread 16 columns; there is a maximum overall length of 256 Bytes; After considering this (and concluding there were no problems) I created the PRIMARY KEY: ALTER TABLE `clients` ADD PRIMARY KEY (`uid`, `server`); If we wanted to have an UNIQUE KEY we should executed.

The UNIQUE constraint ensures that all values in a column are different.

Both the UNIQUE and PRIMARY KEY constraints provide a guarantee for uniqueness for a column or set of columns.

A PRIMARY KEY constraint automatically has a UNIQUE constraint.

However, you can have many UNIQUE constraints per table, but only one PRIMARY KEY constraint per table.

SQL UNIQUE Constraint on CREATE TABLE

The following SQL creates a UNIQUE constraint on the 'ID' column when the 'Persons' table is created:

SQL Server / Oracle / MS Access:

CREATE TABLE Persons (
ID int NOT NULL UNIQUE,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int
);

MySQL:

CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
UNIQUE (ID)
);

To name a UNIQUE constraint, and to define a UNIQUE constraint on multiple columns, use the following SQL syntax:

MySQL / SQL Server / Oracle / MS Access:

CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
CONSTRAINT UC_Person UNIQUE (ID,LastName)
);

SQL UNIQUE Constraint on ALTER TABLE

To create a UNIQUE constraint on the 'ID' column when the table is already created, use the following SQL:

MySQL / SQL Server / Oracle / MS Access:

To name a UNIQUE constraint, and to define a UNIQUE constraint on multiple columns, use the following SQL syntax:

MySQL / SQL Server / Oracle / MS Access:

ALTER TABLE Persons
ADD CONSTRAINT UC_Person UNIQUE (ID,LastName);

DROP a UNIQUE Constraint

To drop a UNIQUE constraint, use the following SQL:

MySQL:

Creating Unique Key In Mysql

SQL Server / Oracle / MS Access:


How To Create Unique Key In Mysql

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DROP DATABASE

DROP TABLE

COPY TABLE WITH CONSTRAINTS

INSERT

DELETE

ALTER. DROP

ALTER. CHANGE

ALTER. DROP. FOREIGN KEY

ALTER. DROP. UNIQUE KEY

ALTER. DROP. PRIMARY KEY

DROP PROCEDURE

DROP FUNCTION

DROP VIEW

DROP TRIGGER

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