You can make an existing column of PostgreSQL Table as PRIMARY KEY using ALTER TABLE query and adding a constraint. Example. As of version 9.4, PostgreSQL supports ALTER TABLE ... ALTER CONSTRAINT for foreign keys. 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.) ; Use ALTER TABLE command to add the needed FOREIGN KEY‘s back to the table. If you want to let PostgreSQL generate the index name, use ALTER TABLE tablename ADD UNIQUE (columns);. ; Verify new keys are in place and updated. Make a Column as PRIMARY KEY. Current Structure. For example, the following PostgreSQL statement creates a new table called COMPANY5 and adds five columns. Which table needs to be operated explicitly Modify the table. The tool then generates the appropriate alter table SQL command for adding the constraint to the table. The name (possibly schema-qualified) of an existing table to alter. PostgreSQL – Make an existing column as PRIMARY KEY. * 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. So not what you are 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; With the below table structure, we can see three FOREIGN KEY constraints. If ONLY is specified, only that table is altered. 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. If ONLY is not specified, the table and all its descendant tables (if any) are updated. table. If the condition evaluates to false, the record violates the constraint and is not entered into the table. Consider the following table named students. 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. We will follow this order to update the FOREIGN KEY‘s.. Use ALTER TABLE command to drop any existing FOREIGN KEY‘s. Looking at your question I think that is (kind of) what you have been looking for. The RazorSQL alter table tool includes an Add Constraint option for adding check constraints to PostgreSQL database tables. The following illustrates the basic syntax of the ALTER TABLE statement: Delete constraint [syntax general] alter table table_name drop constraint “some_name”; Notes: 1. PostgreSQL 11.2 add constraints, delete constraints, add columns, delete columns. Here, we add a CHECK with SALARY column, so … No column in this table is marked PRIMARY KEY. 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. Photo by Richard Payette on Unsplash Steps. – jpmc26 Nov 26 '14 at 1:41 6 Now, we will make the column id as PRIMARY KEY. To change the structure of an existing table, you use PostgreSQL ALTER TABLE statement.. 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