SQL PRIMARY KEY Constraint - W3Schools
SQL PRIMARY KEY Constraint The PRIMARY KEY constraint is used to uniquely identify each record in a table. Primary keys must contain unique values, and cannot contain NULL values. Each table …
MySQL PRIMARY KEY Constraint - W3Schools
MySQL PRIMARY KEY Constraint The PRIMARY KEY constraint uniquely identifies each record in a table. Primary keys must contain UNIQUE values, and cannot contain NULL values. A table can …
SQL FOREIGN KEY Constraint - W3Schools
The FOREIGN KEY constraint is used to prevent actions that would destroy links between tables. A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in …
Python MySQL Create Table - W3Schools
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MySQL UNIQUE Constraint - W3Schools
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.
PHP MySQL Create Table - W3Schools
The column with PRIMARY KEY setting is often an ID number, and is often used with AUTO_INCREMENT Each table should have a primary key column (in this case: the "id" column).
MySQL CREATE TABLE Statement - W3Schools
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PostgreSQL Create Table - W3Schools
To create a new database table using the SQL Shell, make sure you are connected to the database. If not, follow the steps in the Get Started chapter of this tutorial.
SQL Tutorial - W3Schools
SQL is a standard language for storing, manipulating and retrieving data in databases. Our SQL tutorial will teach you how to use SQL in: MySQL, SQL Server, MS Access, Oracle, Sybase, Informix, …
SQL ALTER TABLE Statement - W3Schools
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