CREATE TABLE country_languages (įOREIGN KEY (country_id) REFERENCES countries (country_id)įOREIGN KEY (language_id) REFERENCES languages (language_id) The following statement creates the country_languages table whose primary key consists of two columns. However, for tables that the primary keys consist of more than one column, you must use PRIMARY KEY table constraint to define primary keys. It is possible to use the PRIMARY KEY table constraint to define the primary key that consists of one column as shown in the following statement: CREATE TABLE languages ( CREATE TABLE countries (īecause the primary key of the countries table has only one column, we defined the primary key using PRIMARY KEY column constraint. The following statement creates a table named countries which has country_id column as the primary key.
SQL DEFINE PRIMAR YKEY CODE
) Code language: SQL (Structured Query Language) ( sql ) Creating SQLite primary key examples It is faster than using a primary key which is not an alias of the rowid.Īnother important note is that if you declare a column with the INTEGER type and PRIMARY KEY DESC clause, this column will not become an alias for the rowid column: CREATE TABLE table( Notice that if you assign another integer type such as BIGINT and UNSIGNED INT to the primary key column, this column will not be an alias for the rowid column.īecause the rowid table organizes its data as a B-tree, querying and sorting data of a rowid table are very fast. If a table has the primary key that consists of one column, and that column is defined as INTEGER then this primary key column becomes an alias for the rowid column. Tables that have rowid columns are called rowid tables. The rowid column is a key that uniquely identifies the rows in the table. When you create a table without specifying the WITHOUT ROWID option, SQLite adds an implicit column called rowid that stores 64-bit signed integer. However, to make the current version of SQLite compatible with the earlier version, SQLite allows the primary key column to contain NULL values. It means that the primary key column has an implicit NOT NULL constraint. In SQL standard, the primary key column must not contain NULL values. ) Code language: SQL (Structured Query Language) ( sql ) Second, in case primary key consists of two or more columns, you use the PRIMARY KEY table constraint to define the primary as shown in the following statement. SQLite allows you to define primary key in two ways:įirst, if the primary key has only one column, you use the PRIMARY KEY column constraint to define the primary key as follows: CREATE TABLE table_name( Each table has one and only one primary key. Introduction to SQLite primary keyĪ primary key is a column or group of columns used to identify the uniqueness of rows in a table.
SQL DEFINE PRIMAR YKEY HOW TO
Summary: in this tutorial, you will learn how to use SQLite PRIMARY KEY constraint to define a primary key for a table.
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