如何忽略 PostgreSQL 中区分大小写的行

Question

I know this question may duplicate but i really got confused since I'm new to PostgreSQL. I'm trying to store emails which must not be case sensitive. For example Johndoe@gmail.com must be identical with JoHnDoE@gmail.com in PostgreSQL but i can't find any solution. I know about lower() function, But i don't want use it.

Any solution? Or this is not possible at all in PostgreSQL? I'm using pgAdmin 4

Answer 1

Use Non deterministic collation (only PostgreSQL version >= 12):

From https://dba.stackexchange.com/questions/101294/how-to-create-postgres-db-with-case-insensitive-collation :

CREATE COLLATION ndcoll (provider = icu, locale = 'und', deterministic = false);
CREATE COLLATION case_insensitive (provider = icu, locale = 'und-u-ks-level2', deterministic = false);
CREATE COLLATION ignore_accents (provider = icu, locale = 'und-u-ks-level1-kc-true', deterministic = false);

Edit

From https://stackoverflow.com/a/59101567/2928168 :

    CREATE COLLATION case_insensitive (
      provider = icu,
      locale = 'und-u-ks-level2',
      deterministic = false
    );

    CREATE TABLE names(
      first_name text,
      /* Example collation used in schema directly */
      last_name text COLLATE "case_insensitive",
    );

    insert into names values
      ('Anton','Egger'),
      ('Berta','egger'),
      ('Conrad','Egger');

    select * from names
      order by
        last_name,
        /* Example collation used only in some query */
        first_name collate case_insensitive;

Answer 2

Useupper() in both members of the comparison.

Answer 3

Use ILIKE operator (or its equivalent ~~* for ILIKE and !~~* for NOT ILIKE ).