server: ensure uniqueness on post links

server/migrations/20241225054216_post-link-unique.down.sql

@@ -0,0 +1,3 @@
+-- Add down migration script here
+ALTER TABLE
+    post DROP CONSTRAINT post_link_key;

server/migrations/20241225054216_post-link-unique.up.sql

@@ -0,0 +1,28 @@
+WITH dupes AS (
+    SELECT
+        uid,
+        link,
+        Row_number() over(
+            PARTITION by link
+            ORDER BY
+                link
+        ) AS RowNumber
+    FROM
+        post
+)
+DELETE FROM
+    post
+WHERE
+    uid IN (
+        SELECT
+            uid
+        FROM
+            dupes
+        WHERE
+            RowNumber > 1
+    );
+
+ALTER TABLE
+    post
+ADD
+    UNIQUE (link);