diff --git a/schema.sql b/migrations/0000_initial.sql
similarity index 50%
rename from schema.sql
rename to migrations/0000_initial.sql
index 5b4b114..3790150 100644
--- a/schema.sql
+++ b/migrations/0000_initial.sql
@@ -1,27 +1,20 @@
-DROP TABLE IF EXISTS post_tags;
-DROP TABLE IF EXISTS posts;
-DROP TABLE IF EXISTS series;
-DROP TABLE IF EXISTS tags;
-DROP TABLE IF EXISTS categories;
-DROP TABLE IF EXISTS pages;
-DROP TABLE IF EXISTS settings;
-DROP TABLE IF EXISTS users;
-DROP TABLE IF EXISTS attachments;
+-- BlogFlare baseline. This migration is safe to apply to a fresh database and
+-- to databases previously initialized from the legacy schema.sql file.
 
-CREATE TABLE users (
+CREATE TABLE IF NOT EXISTS users (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
   username TEXT NOT NULL UNIQUE,
   password_hash TEXT NOT NULL,
   created_at DATETIME DEFAULT CURRENT_TIMESTAMP
 );
 
-CREATE TABLE categories (
+CREATE TABLE IF NOT EXISTS categories (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
   name TEXT NOT NULL UNIQUE,
   slug TEXT NOT NULL UNIQUE
 );
 
-CREATE TABLE series (
+CREATE TABLE IF NOT EXISTS series (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
   name TEXT NOT NULL UNIQUE COLLATE NOCASE,
   slug TEXT NOT NULL UNIQUE,
@@ -29,7 +22,7 @@ CREATE TABLE series (
   created_at DATETIME DEFAULT CURRENT_TIMESTAMP
 );
 
-CREATE TABLE posts (
+CREATE TABLE IF NOT EXISTS posts (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
   slug TEXT NOT NULL UNIQUE,
   title TEXT NOT NULL,
@@ -46,9 +39,10 @@ CREATE TABLE posts (
   FOREIGN KEY (series_id) REFERENCES series(id) ON DELETE SET NULL
 );
 
-CREATE INDEX idx_posts_series_order ON posts(series_id, series_weight, published_at, id);
+CREATE INDEX IF NOT EXISTS idx_posts_series_order
+  ON posts(series_id, series_weight, published_at, id);
 
-CREATE TABLE pages (
+CREATE TABLE IF NOT EXISTS pages (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
   slug TEXT NOT NULL UNIQUE,
   title TEXT NOT NULL,
@@ -59,12 +53,12 @@ CREATE TABLE pages (
   FOREIGN KEY (author_id) REFERENCES users(id)
 );
 
-CREATE TABLE tags (
+CREATE TABLE IF NOT EXISTS tags (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
   name TEXT NOT NULL UNIQUE
 );
 
-CREATE TABLE post_tags (
+CREATE TABLE IF NOT EXISTS post_tags (
   post_id INTEGER NOT NULL,
   tag_id INTEGER NOT NULL,
   PRIMARY KEY (post_id, tag_id),
@@ -72,14 +66,14 @@ CREATE TABLE post_tags (
   FOREIGN KEY (tag_id) REFERENCES tags(id) ON DELETE CASCADE
 );
 
-CREATE TABLE settings (
+CREATE TABLE IF NOT EXISTS settings (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
   key TEXT NOT NULL UNIQUE,
   value TEXT NOT NULL,
   updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
 );
 
-CREATE TABLE attachments (
+CREATE TABLE IF NOT EXISTS attachments (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
   filename TEXT NOT NULL,
   key TEXT NOT NULL UNIQUE,
@@ -88,36 +82,56 @@ CREATE TABLE attachments (
   created_at DATETIME DEFAULT CURRENT_TIMESTAMP
 );
 
--- Insert a default user
-INSERT INTO users (username, password_hash) VALUES ('admin', 'admin');
+INSERT OR IGNORE INTO users (username, password_hash) VALUES ('admin', 'admin');
 
--- Insert default categories
-INSERT INTO categories (name, slug) VALUES ('默认分类', 'uncategorized'), ('技术分享', 'tech'), ('生活随笔', 'life');
+INSERT OR IGNORE INTO categories (name, slug) VALUES
+  ('默认分类', 'uncategorized'),
+  ('技术分享', 'tech'),
+  ('生活随笔', 'life');
 
--- Insert dummy posts
-INSERT INTO posts (slug, title, content, author_id, category_id) VALUES 
-('hello-world', 'Hello, BlogFlare!', 'This is my first post on BlogFlare.
+INSERT OR IGNORE INTO posts (slug, title, content, author_id, category_id) VALUES
+  (
+    'hello-world',
+    'Hello, BlogFlare!',
+    'This is my first post on BlogFlare.
 <!--more-->
 Welcome to my new blog powered by **SvelteKit** and **Cloudflare D1**.
 
 > [!NOTE]
 > This is a DoIt style admonition!
 
-It is incredibly fast and cheap to host.', 1, 2),
-('void-theme', 'The Beauty of VOID', 'Typography is essential.
+It is incredibly fast and cheap to host.',
+    (SELECT id FROM users WHERE username = 'admin'),
+    (SELECT id FROM categories WHERE slug = 'tech')
+  ),
+  (
+    'void-theme',
+    'The Beauty of VOID',
+    'Typography is essential.
 <!--more-->
-Typecho Theme VOID inspired this design. It uses a very clean layout.', 1, 2);
+Typecho Theme VOID inspired this design. It uses a very clean layout.',
+    (SELECT id FROM users WHERE username = 'admin'),
+    (SELECT id FROM categories WHERE slug = 'tech')
+  );
 
-INSERT INTO tags (name) VALUES ('Welcome'), ('Design');
-INSERT INTO post_tags (post_id, tag_id) VALUES (1, 1), (2, 2);
+INSERT OR IGNORE INTO tags (name) VALUES ('Welcome'), ('Design');
 
--- Insert default aliases settings
-INSERT INTO settings (key, value) VALUES 
-('alias.post', '文章'),
-('alias.category', '分类'),
-('alias.tag', '标签'),
-('alias.series', '系列'),
-('alias.page', '页面'),
-('site.title', 'BlogFlare'),
-('site.description', 'A high-performance blog powered by Cloudflare D1, R2, and KV.'),
-('r2.public_domain', 'https://assets.yourdomain.com');
+INSERT OR IGNORE INTO post_tags (post_id, tag_id) VALUES
+  (
+    (SELECT id FROM posts WHERE slug = 'hello-world'),
+    (SELECT id FROM tags WHERE name = 'Welcome')
+  ),
+  (
+    (SELECT id FROM posts WHERE slug = 'void-theme'),
+    (SELECT id FROM tags WHERE name = 'Design')
+  );
+
+INSERT OR IGNORE INTO settings (key, value) VALUES
+  ('alias.post', '文章'),
+  ('alias.category', '分类'),
+  ('alias.tag', '标签'),
+  ('alias.series', '系列'),
+  ('alias.page', '页面'),
+  ('site.title', 'BlogFlare'),
+  ('site.description', 'A high-performance blog powered by Cloudflare D1 and R2.'),
+  ('r2.public_domain', 'https://assets.yourdomain.com');
diff --git a/migrations/0001_add_series.sql b/migrations/0001_add_series.sql
index 4b9c4cf..66a5222 100644
--- a/migrations/0001_add_series.sql
+++ b/migrations/0001_add_series.sql
@@ -1,4 +1,8 @@
-CREATE TABLE series (
+-- Compatibility migration for installations that already used schema.sql.
+-- The baseline now contains the final posts shape, so this migration must not
+-- issue non-idempotent ALTER TABLE statements.
+
+CREATE TABLE IF NOT EXISTS series (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
   name TEXT NOT NULL UNIQUE COLLATE NOCASE,
   slug TEXT NOT NULL UNIQUE,
@@ -6,9 +10,7 @@ CREATE TABLE series (
   created_at DATETIME DEFAULT CURRENT_TIMESTAMP
 );
 
-ALTER TABLE posts ADD COLUMN series_id INTEGER REFERENCES series(id) ON DELETE SET NULL;
-ALTER TABLE posts ADD COLUMN series_weight INTEGER;
-
-CREATE INDEX idx_posts_series_order ON posts(series_id, series_weight, published_at, id);
+CREATE INDEX IF NOT EXISTS idx_posts_series_order
+  ON posts(series_id, series_weight, published_at, id);
 
 INSERT OR IGNORE INTO settings (key, value) VALUES ('alias.series', '系列');