From 3de167ae2da9e6d06d952b2c8f34eafaf7a32c32 Mon Sep 17 00:00:00 2001
From: Jeremy Daly <jeremy@jeremydaly.com>
Date: Wed, 17 Jul 2019 10:56:52 -0400
Subject: [PATCH] add documentation around null transaction queries

---
 README.md | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/README.md b/README.md
index 69efb4c..77b7e7d 100644
--- a/README.md
+++ b/README.md
@@ -243,6 +243,24 @@ let results = await mysql.transaction()
   .commit() // execute the queries
 ```
 
+You can also return a `null` or empty response from `.query()` calls within a transaction. This lets you perform conditional transactions like this:
+
+```javascript
+let results = await mysql.transaction()
+  .query('DELETE FROM table WHERE id = ?', [someVar])
+  .query((r) => {
+    if (r.affectedRows > 0) {
+      ['UPDATE anotherTable SET x = 1 WHERE id = ?', [someVar]]
+    } else {
+      return null
+    }
+  })
+  .rollback(e => { /* do something with the error */ }) // optional
+  .commit() // execute the queries
+```
+
+If the record to `DELETE` doesn't exist, the `UPDATE` will not be performed. If the `UPDATE` fails, the `DELETE` will be rolled back.
+
 **NOTE:** Transaction support is designed for InnoDB tables (default). Other table types may not behave as expected.
 
 ## Reusing Persistent Connections