Add partial unique index on project_authorizations

Changelog: changed

db/post_migrate/20230802092922_add_unique_index_project_authorizations_on_unique_project_user.rb

+# frozen_string_literal: true
+
+class AddUniqueIndexProjectAuthorizationsOnUniqueProjectUser < Gitlab::Database::Migration[2.1]
+  INDEX_NAME = 'index_unique_project_authorizations_on_unique_project_user'
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :project_authorizations,
+      %i[project_id user_id],
+      unique: true,
+      where: "is_unique",
+      name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index_by_name :project_authorizations, INDEX_NAME
+  end
+end

db/schema_migrations/20230802092922

+e43d57a88d6dce76867753e349850c7d405397c3356b263ced5ffb47922850f1
\ No newline at end of file

db/structure.sql

@@ -33480,6 +33480,8 @@ CREATE UNIQUE INDEX index_unique_ci_runner_projects_on_runner_id_and_project_id
 CREATE UNIQUE INDEX index_unique_issue_metrics_issue_id ON issue_metrics USING btree (issue_id);
+CREATE UNIQUE INDEX index_unique_project_authorizations_on_unique_project_user ON project_authorizations USING btree (project_id, user_id) WHERE is_unique;
+
 CREATE INDEX index_unit_test_failures_failed_at ON ci_unit_test_failures USING btree (failed_at DESC);
 CREATE UNIQUE INDEX index_unit_test_failures_unique_columns ON ci_unit_test_failures USING btree (unit_test_id, failed_at DESC, build_id);