SQLite Create Table
Summary: in this tutorial, you will learn how to create new tables using SQLite CREATE TABLE
statement using various options.
Introduction to SQLite CREATE TABLE
statement
To create a new table in SQLite, you use CREATE TABLE
statement using the following syntax:
CREATE TABLE [IF NOT EXISTS] [schema_name].table_name (
column_1 data_type PRIMARY KEY,
column_2 data_type NOT NULL,
column_3 data_type DEFAULT 0,
table_constraints
) [WITHOUT ROWID];
In this syntax:
- First, specify the name of the table that you want to create after the
CREATE TABLE
keywords. The name of the table cannot start withsqlite_
because it is reserved for the internal use of SQLite. - Second, use
IF NOT EXISTS
option to create a new table if it does not exist. Attempting to create a table that already exists without using theIF NOT EXISTS
option will result in an error. - Third, optionally specify the
schema_name
to which the new table belongs. The schema can be the main database,temp
database or any attached database. - Fourth, specify the column list of the table. Each column has a name, data type, and the column constraint. SQLite supports
PRIMARY KEY
,UNIQUE
,NOT NULL
, andCHECK
column constraints. - Fifth, specify the table constraints such as
PRIMARY KEY
,FOREIGN KEY
,UNIQUE
, andCHECK
constraints. - Finally, optionally use the
WITHOUT ROWID
option. By default, a row in a table has an implicit column, which is referred to as therowid
,oid
or_rowid_
column. Therowid
column stores a 64-bit signed integer key that uniquely identifies the row inside the table. If you don’t want SQLite creates therowid
column, you specify theWITHOUT ROWID
option. A table that contains therowid
column is known as arowid
table. Note that theWITHOUT ROWID
option is only available in SQLite 3.8.2 or later.
Note that the primary key of a table is a column or a group of columns that uniquely identify each row in the table.
SQLite CREATE TABLE
examples
Suppose you have to manage contacts using SQLite.
Each contact has the following information:
- First name
- Last name
- Phone
The requirement is that the email and phone must be unique. In addition, each contact belongs to one or many groups, and each group can have zero or many contacts.
Based on these requirements, we came up with three tables:
- The
contacts
table that stores contact information. - The
groups
table that stores group information. - The
contact_groups
table that stores the relationship between contacts and groups.
The following database diagram illustrates tables:contacts
groups
, and contact_groups.
The following statement creates the contacts
table.
CREATE TABLE contacts (
contact_id INTEGER PRIMARY KEY,
first_name TEXT NOT NULL,
last_name TEXT NOT NULL,
email TEXT NOT NULL UNIQUE,
phone TEXT NOT NULL UNIQUE
);
The contact_id
is the primary key of the contacts
table.
Because the primary key consists of one column, you can use the column constraint.
The first_name
and last_name
columns have TEXT
storage class and these columns are NOT NULL
. It means that you must provide values when you insert or update rows in the contacts
table.
The email and phone are unique therefore we use the UNIQUE
constraint for each column.
The following statement creates the groups
table:
CREATE TABLE groups (
group_id INTEGER PRIMARY KEY,
name TEXT NOT NULL
);
The groups
table is quite simple with two columns: group_id
and name
. The group_id
column is the primary key column.
The following statement creates contact_groups
table:
CREATE TABLE contact_groups(
contact_id INTEGER,
group_id INTEGER,
PRIMARY KEY (contact_id, group_id),
FOREIGN KEY (contact_id)
REFERENCES contacts (contact_id)
ON DELETE CASCADE
ON UPDATE NO ACTION,
FOREIGN KEY (group_id)
REFERENCES groups (group_id)
ON DELETE CASCADE
ON UPDATE NO ACTION
);
The contact_groups
table has a primary key that consists of two columns: contact_id
and group_id
.
To add the table primary key constraint, you use this syntax:
PRIMARY KEY (contact_id, group_id)
In addition, the contact_id
and group_id
are the foreign keys. Therefore, you use FOREIGN KEY
constraint to define a foreign key for each column.
FOREIGN KEY (contact_id)
REFERENCES contacts (contact_id)
ON DELETE CASCADE
ON UPDATE NO ACTION
FOREIGN KEY (group_id)
REFERENCES groups (group_id)
ON DELETE CASCADE
ON UPDATE NO ACTION
Note that we will discuss in the FOREIGN KEY
constraint in detail in the subsequent tutorial.
In this tutorial, you have learned how to create a new table with various options using SQLite CREATE TABLE
statement.