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3. Create A Unique Key In Mysql
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1. Therefore, I decided to try and solve this issue using a MySQL query. The query I need should simply generate a 8-character alphanumeric string which is not already in the table. I thought of the generate&check loop approach again, but I'm not limiting this question to that just in case there's a.
2. I want to generate a unique primary key, something similar to the auto increment feature, but i do not want it to be auto increment. The reasoning for this is: this table will have rows deleted by the hundreds every day, and maybe even thousands in a few years (I hope!), All the while having more rows replace the ones that were erased.

SQL UNIQUE Constraint

Jul 05, 2011  All 'random' methods can lead to performance issues due to jumping around in the table. This probably won't be an issue until you have millions of users. How to Use Unique Indexes in MySQL and Other Databases If you’ve been using databases for a while, you’ve probably set a primary key in most of your tables. A primary key is a unique. Thread. How to generate unique primary key in MySQL? Yuan edit: 28 Apr. Re: How to generate unique primary key in MySQL? Yuan edit: 28 Apr. Re: How to.

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.

Mysql Delete Unique Key

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:

SQL Server / Oracle / MS Access:

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RENAME DATABASE

RENAME TABLE

COPY TABLE WITHOUT CONSTRAINTS

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SELECT

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DELETE

ALTER.. DROP

ALTER.. CHANGE

ALTER.. DROP.. FOREIGN KEY