With the below table structure, we can see three FOREIGN KEY constraints. – jpmc26 Nov 26 '14 at 1:41 6 ; Use ALTER TABLE command to add the needed FOREIGN KEY‘s back to the table. The tool then generates the appropriate alter table SQL command for adding the constraint to the table. You can make an existing column of PostgreSQL Table as PRIMARY KEY using ALTER TABLE query and adding a constraint. Photo by Richard Payette on Unsplash Steps. * can be appended to the table name to indicate that descendant tables are to be scanned, but in the current version, this is the default behavior. Which table needs to be operated explicitly Delete constraint [syntax general] alter table table_name drop constraint “some_name”; Notes: 1. ; Verify new keys are in place and updated. If the condition evaluates to false, the record violates the constraint and is not entered into the table. As of version 9.4, PostgreSQL supports ALTER TABLE ... ALTER CONSTRAINT for foreign keys. Now, we will make the column id as PRIMARY KEY. ALTER TABLE distributors DROP CONSTRAINT zipchk , ADD CONSTRAINT zipchk CHECK (length(zipcode) = 6); ALTER CONSTRAINT in Postgres 9.4 or later (like you found) can only change the "deferability" of a FK constraints. table. The RazorSQL alter table tool includes an Add Constraint option for adding check constraints to PostgreSQL database tables. Current Structure. If ONLY is not specified, the table and all its descendant tables (if any) are updated. To change the structure of an existing table, you use PostgreSQL ALTER TABLE statement.. I have a table in PostgreSQL where the schema looks like this: CREATE TABLE "foo_table" ( "id" serial NOT NULL PRIMARY KEY, "permalink" varchar(200) NOT NULL, "text" varchar(512) NOT NULL, "timestamp" timestamp with time zone NOT NULL ) Now I want to make the permalink unique across the table by ALTER-ing the table. If you want to let PostgreSQL generate the index name, use ALTER TABLE tablename ADD UNIQUE (columns);. Example. PostgreSQL – Make an existing column as PRIMARY KEY. Modify the table. The name (possibly schema-qualified) of an existing table to alter. Consider the following table named students. Looking at your question I think that is (kind of) what you have been looking for. Well, this not directly altering FOREIGN KEY constraint, and there are DROP and ADD still, though this is only one statement: ALTER table chemlab.rule_header DROP CONSTRAINT rule_header_parent_id_fkey, ADD CONSTRAINT rule_header_parent_id_fkey FOREIGN KEY (parent_id) REFERENCES chemlab.rule_header(id) ON DELETE RESTRICT; The add constraint function allows the user to add a constraint name and a constraint condition. The following illustrates the basic syntax of the ALTER TABLE statement: Here, we add a CHECK with SALARY column, so … Summary: in this tutorial, you will learn how to use the PostgreSQL ALTER TABLE statement to modify the structure of a table.. Introduction to PostgreSQL ALTER TABLE statement. Make a Column as PRIMARY KEY. For example, the following PostgreSQL statement creates a new table called COMPANY5 and adds five columns. So not what you are looking for. If ONLY is specified, only that table is altered. We will follow this order to update the FOREIGN KEY‘s.. Use ALTER TABLE command to drop any existing FOREIGN KEY‘s. This features will "Allow constraint attributes to be altered, so the default setting of NOT DEFERRABLE can be altered to DEFERRABLE and back." (Note that the CONSTRAINT keyword must be omitted.) 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