Deferrable, case-insensitive unique constraint

Question

Is it possible in PostgreSQL to create a deferrable unique constraint on a character column, but case-insensitive?

Let\'s assume the following basic table:

Answer 1

You can circumvent the restriction by using the special type citext provided by the additional module of the same name. Quoting the manual:

The citext module provides a case-insensitive character string type, citext. Essentially, it internally calls lower when comparing values. Otherwise, it behaves almost exactly like text.

It addresses your case exactly. Run once per database:

CREATE EXTENSION citext;

Then you can:

CREATE TABLE sample_table ( 
   my_column citext
  ,CONSTRAINT my_unique_constraint UNIQUE(my_column)
   DEFERRABLE INITIALLY IMMEDIATE
);