安装ORACLE数据库软件，dbca安装数据库后，需要配置listener连接数据库。这里有一些概念比较难理解，记录一些分析实战结论。
从连接端讲起。
1 连接数据库的方式
oracle的连接串有几部分构成，这里就按sqlplus为例，一个完成的连接串遵循下面格式
sqlplus 用户名/密码@主机:端口号/SID 可选as sysdba下面先讲只有listener没有tns的情况
2 listener
使用listener连接需要配置完整连接信息，这里分为两种连接方式，我们看一个listener的例子：
（带sid的listener使用netmgr增加listener的datavase services即可出现sid的配置）
LISTENER2 =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = iZbp1d4tisi44j6vxze02fZ)(PORT = 1522))
)
SID_LIST_LISTENER2 =
(SID_LIST =
(SID_DESC =
(GLOBAL_DBNAME = gdn1400)
(ORACLE_HOME = /fdisk1/oracle1400/base/dbhome_1)
(SID_NAME = orcl1400)
)
)
ADR_BASE_LISTENER2 = /fdisk1/oracle1400/base
LISTENER1 =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = iZbp1d4tisi44j6vxze02fZ)(PORT = 1521))
)
ADR_BASE_LISTENER1 = /fdisk1/oracle1400/base这里有两个listener，有sid的叫做静态listener，没有sid的叫做动态listener。在查看状态时存在区别：
lsnrctl status listener1
...
Services Summary...
Service "orcl1400" has 1 instance(s).
Instance "orcl1400", status READY, has 1 handler(s) for this service...
Service "orcl1400XDB" has 1 instance(s).
Instance "orcl1400", status READY, has 1 handler(s) for this service...
The command completed successfully
lsnrctl status listener2
...
Services Summary...
Service "gdn1400" has 1 instance(s).
Instance "orcl1400", status UNKNOWN, has 1 handler(s) for this service...
The command completed successfully注意对于lsnrctl来说，service的名字是global database name
我们在看一个连接串：
sqlplus sys/password@iZbp1d4tisi44j6vxze02fZ:1521/orcl1400 as sysdba这个连接串中最需要关注的就是服务名了，这里是orcl1400。
注意！：这个服务名必须由listener中的某一个提供，这里listener2的服务名提供的是gdn1400，而listener1没有提供服务名。那么如何连接数据库呢？答案就是走listener1的连接会去数据库中动态的查询服务名（所以叫做动态连接）
SQL> show parameter service
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
service_names string orcl1400也就是为什么使用orcl1400能连上数据库。这里我们使用静态连接试一下，也是可以连接数据库的（注意端口号和动态的不同）
sqlplus sys/password@iZbp1d4tisi44j6vxze02fZ:1522/gdn1400 as sysdba
SQL*Plus: Release 12.1.0.2.0 Production on Thu May 30 20:51:00 2019
Copyright (c) 1982, 2014, Oracle. All rights reserved.
Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
SQL>3 TNS
那么tns是什么呢？我们看下这个连接串。
sqlplus sys/password@iZbp1d4tisi44j6vxze02fZ:1521/orcl1400 as sysdba@后面的信息很多，能否省略呢？比如
sqlplus sys/password@tns1400 as sysdba这样看起来简洁很多也便于管理，TNS即实现了这个功能，我们看一个tnsnames.ora的配置：
NSN1522 =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = iZbp1d4tisi44j6vxze02fZ)(PORT = 1522))
)
(CONNECT_DATA =
(SERVICE_NAME = gdn1400)
)
)
NSN1521 =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = iZbp1d4tisi44j6vxze02fZ)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = orcl1400)
)
)这里可以看到，最左面的NSN1522和NSN1521就是我们可以@的服务名字。内部的映射信息是指向listener的，这里的servicename要和上面的global database name对应上！
NSN1522, iZbp1d4tisi44j6vxze02fZ, 1522, gdn1400 -----> listener2
NSN1521, iZbp1d4tisi44j6vxze02fZ, 1521, orcl1400 -----> listener1两个别名指向了两个不同的listener，连接测试：
# sqlplus sys/password@nsn1521 as sysdba
SQL*Plus: Release 12.1.0.2.0 Production on Thu May 30 20:58:51 2019
Copyright (c) 1982, 2014, Oracle. All rights reserved.
Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
SQL>
# sqlplus sys/password@nsn1522 as sysdba
SQL*Plus: Release 12.1.0.2.0 Production on Thu May 30 20:58:55 2019
Copyright (c) 1982, 2014, Oracle. All rights reserved.
Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
SQL>注意：tns依赖lsnrctl使用，可以理解为hostname这样的概念，注意tns的SERVICE_NAME等信息必须和listener关联才能连接！