所以我正在尝试使用 citext，但它似乎是来自 ubuntu 14.04 postgres 安装的 MIA。你在哪里可以找到这个名为 citext for postgresql 9.3 的神秘野兽？
project_test=> CREATE TABLE "customers_addresstype" (
project_test(> "id" serial NOT NULL PRIMARY KEY,
project_test(> "customer_id" integer NOT NULL REFERENCES "customers_customer" ("id") DEFERRABLE INITIALLY DEFERRED,
project_test(> "display" citext NOT NULL,
project_test(> UNIQUE ("customer_id", "display")
project_test(> )
project_test-> ;
ERROR: type "citext" does not exist
LINE 4: "display" citext NOT NULL,
^
project_test=> CREATE EXTENSION IF NOT EXISTS citext WITH SCHEMA ext;
ERROR: could not open extension control file "/usr/share/postgresql/9.3/extension/citext.control": No …