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. If ONLY is specified, only that table is altered. As of version 9.4, PostgreSQL supports ALTER TABLE ... ALTER CONSTRAINT for foreign keys. If you want to let PostgreSQL generate the index name, use ALTER TABLE tablename ADD UNIQUE (columns);. We will follow this order to update the FOREIGN KEY‘s.. Use ALTER TABLE command to drop any existing FOREIGN KEY‘s. Consider the following table named students. 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. 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. Here, we add a CHECK with SALARY column, so … Current Structure. Delete constraint [syntax general] alter table table_name drop constraint “some_name”; Notes: 1. For example, the following PostgreSQL statement creates a new table called COMPANY5 and adds five columns. The following illustrates the basic syntax of the 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. The name (possibly schema-qualified) of an existing table to alter. With the below table structure, we can see three FOREIGN KEY constraints. This might help, although it may be a bit of a dirty hack: create or replace function create_constraint_if_not_exists ( t_name text, c_name text, constraint_sql text ) returns void AS $$ begin -- Look for our constraint if not exists (select constraint_name from information_schema.constraint_column_usage where table_name = t_name and constraint_name = c_name) then execute constraint… Modify the table. 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; PostgreSQL – Make an existing column as PRIMARY KEY. Now, we will make the column id 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. 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. No column in this table is marked PRIMARY KEY. If the condition evaluates to false, the record violates the constraint and is not entered into the table. This features will "Allow constraint attributes to be altered, so the default setting of NOT DEFERRABLE can be altered to DEFERRABLE and back." Make a Column as PRIMARY KEY. ; Verify new keys are in place and updated. (Note that the CONSTRAINT keyword must be omitted.) PostgreSQL 11.2 add constraints, delete constraints, add columns, delete columns. 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