![]() ![]() The constraint name parameter is used to define the foreign key constraint.In the above syntax, we have used the following parameters, which we discussed in the below table: REFERENCES parent_table_name (column_name.) The below illustrations are used to define a foreign key using the CREATE TABLE command in PostgreSQL:įOREIGN KEY (column_name. We can create a foreign key in PostgreSQL with the CREATE TABLE command's help. ![]() Creating a Foreign Key using a CREATE TABLE command Now, we are discussing each one in detail. Note: In PostgreSQL, the ALTER TABLE command is used to add or drop a primary key. In PostgreSQL, we can create a foreign key with the help of the following commands: How to create a Foreign key in PostgreSQL And PostgreSQL allows us to describe a foreign key using the foreign key constraint. Note: A PostgreSQL table can have various foreign keys depending on its connection with other tables. In the parent-child relationship, the parent table keep the initial column values, and the child table's column values reference the parent column values. In other words, we can say that a foreign key makes it possible to generate a parent-child relationship with the tables. PostgreSQL foreign key constraint specifies the values in a group of columns or a column in the Child table, equivalent to the values in a group of columns or a column of the Parent table. In PostgreSQL, the foreign key's values is parallel to the actual values of the primary key in the other table that's why it is also known as Referential integrity Constraint. The foreign key is also known as the referencing key, and it matches the primary key field from another table, which implies that the foreign key field in one table refers to the other table's primary key field. It is used to have the value in one column or group of columns displayed in the same column or combination of columns in another table. What is PostgreSQL Foreign key / Foreign Key Constraint?Ī foreign key is a group of columns with values dependent on the primary key benefits from another table. You can run the script once.In this section, we are going to understand the working of the PostgreSQL Foreign Key, the examples of PostgreSQL Foreign key, how to add the PostgreSQL Foreign key into the tables using foreign key constraints. ![]() 'ALTER TABLE %s ALTER CONSTRAINT %s DEFERRABLE INITIALLY DEFERRED ',Īnd conrelid = any(array::regclass)Īnd connamespace = 'ssp2_pcat'::regnamespace You can generate a script to alter foreign keys to DEFERRABLE INITIALLY DEFERRED in this way: select format( There are more options, however, so read about deferrable constraints in the documentation: It's enough when you define foreign keys as deferrable initially deferred and execute all inserts in a single transaction. You don't need to drop and recreate foreign keys. Can someone please keep me posted if I'm missing any join from any other data dictionary tables? UPPER(cs.TABLE_NAME) = 'ADDITIONAL_RULES' ANDīut unfortunately this query is not giving the desired result, looks like I'm missing something as its especially when selecting the c.COLUMN_NAMEfield instead of the references field it's giving all the available fields in the table, also it's not giving the name of the Parent_table cs.TABLE_NAME rather it's giving the same table_name. WHERE cs.CONSTRAINT_NAME = rc.CONSTRAINT_NAME AND ' REFERENCES ' ||cs.TABLE_NAME || ' (' || cs.CONSTRAINT_NAME || ') ' || ' ON UPDATE ' || rc.UPDATE_RULE || ' ON DELETE ' || rc.DELETE_RULEįROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS RC, INFORMATION_SCHEMA.TABLE_CONSTRAINTS CS, INFORMATION_SCHEMA.COLUMNS C ' ADD CONSTRAINT ' ||rc.CONSTRAINT_NAME || ![]() Now I'm working on a similar query to ADD the constraints as follows, (that are dropped in the first step), SELECT DISTINCT 'ALTER TABLE ' || cs.TABLE_NAME || Used the WITH clause with STRING_AGG function by enabling the DBlinkĮxtensions in the POSTGRES similarly using Dynamic SQL so that it gives SQL for multiple tables at one shot. Mentioned above truncate is done as its very straight forward. The output of above SQL is going to be as follows,ĪLTER TABLE SSP2_PCAT.RATES DROP CONSTRAINT fk_rate UPPER(CONSTRAINT_SCHEMA) = 'SSP2_PCAT' AND 'ALTER TABLE SSP2_PCAT.' || TABLE_NAME || ' DROP CONSTRAINT ' || CONSTRAINT_NAME || ' 'įROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS I created the following SQL using dynamic SQL to genarate a SQL DROP foreign key constraint so that I can execute for multiple tables I'm working on, SELECT ADD the constraints that are dropped at the first step. ![]()
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