diff --git a/koa.md b/koa.md
new file mode 100644
index 000000000..fd53bf245
--- /dev/null
+++ b/koa.md
@@ -0,0 +1,94 @@
+---
+title: Koa
+category: Ruby
+---
+
+### Reference
+
+```js
+app.use(function * (next) {
+  var ctx = this
+
+  ctx.request
+  ctx.response
+
+  ctx.body = 'hello'
+
+  ctx.state.user = yield User.find(id).fetch()
+
+  ctx.cookies.set('foo', 'hello', { signed: true })
+  ctx.cookies.get('foo')
+
+  ctx.throw(403)
+```
+
+### Request
+
+```js
+  ctx.header        // ctx.headers
+  ctx.method        // and =
+  ctx.url           // and =
+  ctx.originalUrl
+  ctx.origin        // => 'http://example.com'
+  ctx.href          // => 'http://example.com/foo?q=hello'
+  ctx.path          // and =
+  ctx.query         // { q: 'hello' }
+  ctx.query         // and =
+  ctx.querystring
+  ctx.querystring   // and =
+  ctx.host
+  ctx.hostname
+  ctx.fresh
+  ctx.stale
+  ctx.socket
+  ctx.protocol
+  ctx.secure
+  ctx.ip
+  ctx.ips
+  ctx.subdomains
+  ctx.is()                  // .is('html') .is('text/html')
+  ctx.accepts()             // .accepts('html') .accepts('html', 'json')
+  ctx.acceptsEncodings()    // .acceptsEncodings('gzip')
+  ctx.acceptsCharsets()
+  ctx.acceptsLanguages()
+  ctx.get()
+
+  ctx.request.type          // => 'image/jpg'
+  ctx.request.charset       // => 'utf-8'
+  ctx.request.protocol      // => 'https'
+  ctx.request.secure        // => true
+  ctx.request.ip            // (supports X-Forwarded-For if app.proxy)
+  ctx.request.ips
+  ctx.request.subdomains
+
+  ctx.request.fresh
+  ctx.request.stale
+```
+
+### Response
+
+```js
+  ctx.body = 'hello'
+
+  ctx.throw(403)
+  ctx.throw('name required', 403)
+  ctx.throw(403, 'name required')
+  ctx.throw('oops')
+  ctx.assert(ctx.state.user, 401, 'You must log in')
+```
+
+### Middlewares
+
+```js
+exports.conditionalGet = require('koa-conditional-get');
+exports.responseTime = require('koa-response-time');
+exports.ratelimit = require('koa-ratelimit');
+exports.compress = require('koa-compress');
+exports.rewrite = require('koa-rewrite');
+exports.favicon = require('koa-favicon');
+exports.session = require('koa-session');
+exports.static = require('koa-static');
+exports.logger = require('koa-logger');
+exports.mount = require('koa-mount');
+exports.etag = require('koa-etag');
+```
diff --git a/sql-join.md b/sql-join.md
index 5644a5b27..875e86467 100644
--- a/sql-join.md
+++ b/sql-join.md
@@ -7,13 +7,14 @@ SELECT * FROM order_items LEFT OUTER JOIN orders ON order_items.order_id = order
 ```
 
 ```
-   __  __
- /   /\   \
-| A |u |B  |
- \___\/__ /
+.--------.
+| A  .---+----.
+|    | ∩ |    |
+'----+---'  B |
+     '--------'
 ```
 
-* inner join = `u`
-* left outer join = `A` + `u`
-* right outer join = `u` + `B`
-* full outer join = `A` + `u` + `B`
+* inner join = `∩`
+* left outer join = `A` + `∩`
+* right outer join = `∩` + `B`
+* full outer join = `A` + `∩` + `B`