Sqlite> INSERT INTO track VALUES(14, 'Mr. Sqlite> - does not correspond to row in the artist table. Sqlite> - This fails because the value inserted into the trackartist column (3) The following SQLite command-line session illustrates the effect of the foreign key constraint added to the track table: sqlite> SELECT * FROM artist Refer to the CREATE TABLE documentation for details. There are several other ways to add an equivalent foreign key declaration to a CREATE TABLE statement. Tip: If the application requires a stricter relationship between artist and track, where NULL values are not permitted in the trackartist column, simply add the appropriate "NOT NULL" constraint to the schema. Expressed in SQL, this means that for every row in the track table, the following expression evaluates to true: trackartist IS NULL OR EXISTS(SELECT 1 FROM artist WHERE artistid=trackartist) Attempting to insert a row into the track table that does not correspond to any row in the artist table will fail, as will attempting to delete a row from the artist table when there exist dependent rows in the track table There is one exception: if the foreign key column in the track table is NULL, then no corresponding entry in the artist table is required. This way, the constraint is enforced by SQLite. To do so, a foreign key definition may be added by modifying the declaration of the track table to the following: CREATE TABLE track(įOREIGN KEY(trackartist) REFERENCES artist(artistid) One solution is to add an SQL foreign key constraint to the database schema to enforce the relationship between the artist and track table.
This might cause the application or applications to malfunction later on, or at least make coding the application more difficult. Or rows might be deleted from the artist table, leaving orphaned rows in the track table that do not correspond to any of the remaining rows in artist.
Unfortunately, if a user edits the database using an external tool or if there is a bug in an application, rows might be inserted into the track table that do not correspond to any row in the artist table. After all, the comment in the declaration says so. The applications using this database are entitled to assume that for each row in the track table there exists a corresponding row in the artist table. Trackartist INTEGER - Must map to an artist.artistid! For example, consider a database schema created using the following SQL commands: CREATE TABLE artist( SQL foreign key constraints are used to enforce "exists" relationships between tables.
This may be found as part of the documentation for the CREATE TABLE statement.
Sqlite insert on conflict full#
This document does not contain a full description of the syntax used to create foreign key constraints in SQLite. Finally, section 6 enumerates the missing features and limits of the current implementation. Section 4 describes the advanced foreign key related features supported by SQLite and section 5 describes the way the ALTER and DROP TABLE commands are enhanced to support foreign key constraints.
The next section, section 3, describes the indexes that the user must create in order to use foreign key constraints, and those that should be created in order for foreign key constraints to function efficiently. Section 2 describes the steps an application must take in order to enable foreign key constraints in SQLite (it is disabled by default). The first section introduces the concept of an SQL foreign key by example and defines the terminology used for the remainder of the document. This document describes the support for SQL foreign key constraints introduced in SQLite version 3.6.19 ().
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