Parent_table parameter defines the name of the parent table, followed by its column names, which are referenced by the foreign key. Please note that if you do not specify the foreign key name, PostgreSQL will create the constraint name automatically as per the default naming convention.įk_columns are the table columns to be used as a foreign key. In the Postgres foreign key syntax above, specify the following:Ĭonstraint_name is the name to be used to define the foreign key constraint. Let’s look at how to create a PostgreSQL foreign key when creating a table. How to create a foreign key in PostgreSQL? Actually, you can do it in three ways: define the foreign key inside the CREATE TABLE statement, run a separate ALTER TABLE statement in case you want to add a foreign key to an already existing table, or create a FOREIGN KEY constraint visually in a GUI tool for PostgreSQL. CREATE TABLE sports(Ī PostgreSQL table can have various foreign keys depending on its connection with other tables. In other words, multiple records in the sportspeople table can contain the same sports_id that points to one sports_id value in the sports table. This way, it forms one-to-many relationships between the sportspeople and sports tables, which means that for one sport there could be multiple sportspeople. This foreign key refers to the primary key column sports_id in the sports table. Suppose, we have the sportspeople table that has a PostgreSQL foreign key column sports_id. Foreign key exampleįor better understanding, let us consider the following example. Constraints are the rules enforced on data columns in tables and used to prevent invalid data from being entered into the database. Technically, FOREIGN KEYs, alongside PRIMARY KEYs, CHECK and UNIQUE constraints, belong to the PostgreSQL database constraints. In other words, the foreign key field in one table refers to another table’s primary key field. The foreign key is often called the referencing key as it matches the primary key field from another table. And the table referenced by the foreign key is called the parent table (or the referenced table). The database table that contains a foreign key is called the child table (or the referencing table). Learn the basics of the PostgreSQL FOREIGN KEY constraint What is FOREIGN KEY in PostgreSQL?Ī foreign key (FK) represents one or more than one column used to establish and enforce a link between data in two database tables for controlling data stored in the foreign key table. Here we will go into the basics of PostgreSQL Foreign Keys, demonstrate to you how to create, drop, and manage foreign keys on real-life examples, and introduce to you one of the most convenient Postgres GUI tools on the market. Both primary keys and foreign keys are the two types of constraints that are used to enforce data integrity in PostgreSQL tables. This is the second article in our series on PostgreSQL database constraints, and it comprises a follow-up to our recent PostgreSQL Primary Keys review. Why is a GUI tool a better way to manage keys in PostgreSQL?.Learn the basics of the PostgreSQL FOREIGN KEY constraint.Read on to find out what foreign keys in PostgreSQL are and how to use them. In fact, it is the FOREIGN KEY mechanism that provides the relationality of relational databases. This is because the MyISAM engine doesn’t support adding foreign key constraints, so when you try to add a foreign key constraint to the table, it will trigger the ERROR 1215.Foreign keys help normalize data in databases and reduce redundancy. You need to check whether the existing table and the table you want to create are using InnoDB engine. Make sure your tables are using InnoDB engine Once you are sure you have the correct syntax, let’s check the engine used by your tables next. Once you have the correct syntax, make sure that there’s no typo in, , and or you may trigger the same error. You must replace next to the FOREIGN KEY syntax with the column name in the current table, while and must refer to the table and column name of an existing table.
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