Postgresql: auto lowercase text while (or before) inserting to a column

Question

I want to achieve case insensitive uniqueness in a varchar column. But, there is no case insensitive text data type in Postgres. Since original case of text is not important, it will be a good idea to convert all to lowercase/uppercase before inserting in a column with UNIQUE constraint. Also, it will require one INDEX for quick search.

Is there any way in Postgres to manipulate data before insertion?

I looked at this other question: How to automatically convert a MySQL column to lowercase. It suggests using triggers on insert/update to lowercase text or to use views with lowercased text. But, none of the suggested methods ensure uniqueness.

Also, since this data will be read/written by various applications, lowercasing data in every individual application is not a good idea.

Answer 1

You don't need a case-insensitive data type (although there is one)

CREATE UNIQUE INDEX idx_lower_unique 
   ON your_table (lower(the_column));

That way you don't even have to mess around with the original data.

Answer 2

ALTER TABLE your_table
  ADD CONSTRAINT your_table_the_column_lowercase_ck
  CHECK (the_column = lower(the_column));

From the manual:

The use of indexes to enforce unique constraints could be considered an implementation detail that should not be accessed directly.