Merge pull request #144 from SwanSpouse/database

#65 sql exec order

README.md

@@ -34,10 +34,10 @@ Redis原始源码来自： https://github.com/antirez/redis
 * [hash code](https://github.com/SwanSpouse/redis_go/blob/master/z_docs/framework/hash_code.md)
 * [new redis go server model](https://github.com/SwanSpouse/redis_go/blob/master/z_docs/framework/redis_go_server_model.md)
 
-
 #### 数据库
 * [数据库事务](https://github.com/SwanSpouse/redis_go/blob/master/z_docs/database/db_transaction.md)
 * [数据库锁和索引](https://github.com/SwanSpouse/redis_go/blob/master/z_docs/database/database_index.md)
+* [数据库SQL语句执行顺序](https://github.com/SwanSpouse/redis_go/blob/master/z_docs/database/database_sql_order.md)
 
 #### data type
 * [Hash表实现](https://github.com/SwanSpouse/redis_go/blob/master/z_docs/data_type/redis_go_dict.md)

z_docs/database/database_sql_order.md

@@ -0,0 +1,21 @@
+
+
+#### SQL语句执行顺序
+
+查询中用到的关键词主要包含六个，并且他们的顺序依次为: 
+
+* select --> from --> where --> group by --> having --> order by 
+
+SQL Select语句完整的执行顺序【从DBMS使用者角度】:
+
+1. from:需要从哪个数据表检索数据 
+
+2. where:过滤表中数据的条件 
+
+3. group by:如何将上面过滤出的数据分组 
+
+4. having:对上面已经分组的数据进行过滤的条件 
+
+5. select:查看结果集中的哪个列，或列的计算结果 
+
+6. order by :按照什么样的顺序来查看返回的数据