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LYDongD · Aug 1, 2019 · 22811b5 · 22811b5
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diff --git a/SUMMARY.md b/SUMMARY.md
@@ -150,6 +150,7 @@
       * [多数据源](dev-ops/mysql/multi-db.md)
       * [存储过程](dev-ops/mysql/stored_procedure.md)
       * [oracle常用SQL](dev-ops/mysql/oracle.md)
+      * [索引](dev-ops/mysql/index.md)
     * [计算机原理](dev-ops/computer/README.md)
       * [CPU](dev-ops/computer/cpu.md)
       * [网络](dev-ops/computer/net.md)

diff --git a/dev-ops/mysql/index.md b/dev-ops/mysql/index.md
@@ -0,0 +1,29 @@
+## 索引
+
+### 如何在创建索引时指定索引类型？
+
+mysql支持两种索引：
+
+* B+ tree
+* hash
+
+通过以下语句指定索引类型
+
+```
+create index dx_username using hash on tb_user(username); 
+
+```
+
+然而，innodb并不支持hash索引，如果坚持要指定hash类型，mysql会返回错误：
+
+This storage engine does not support the HASH index algorithm, storage engine default was used instead.
+
+### hash 索引的使用场景
+
+hash索引用hash字典实现，读写速度都很快，但是无法实现范围查询，例如>, between等操作符相关的query
+
+因此，hash索引适合key-value数据库，如果有人拿mysql做key-value存储的话
+
+B+ tree 叶子节点是双向链表，利于范围查询和排序等
+
+