Hive 中变量和属性命名空间
下面我们来用几个例子操作下：
&hive
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/home/hadoop/apache-hive-2.1.0-bin/lib/log4j-slf4j-impl-2.4.1.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/home/hadoop/hadoop/share/hadoop/common/lib/slf4j-log4j12-1.7.10.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.apache.logging.slf4j.Log4jLoggerFactory]
Logging initialized using configuration in jar:file:/home/hadoop/apache-hive-2.1.0-bin/lib/hive-common-2.1.0.jar!/hive-log4j2.properties Async: true
Hive-on-MR is deprecated in Hive 2 and may not be available in the future versions. Consider using a different execution engine (i.e. spark, tez) or using Hive 1.X releases.
1. hive> set env:HOME;
env:HOME=/home/hadoop
this is didsplay /home/user
2. set; and set -v 这两个命令都会打印出hivevar, hiveconf, system, env的变量，但是带-v的命令会在这个的基础上打印出所有定义的属性，如： HDFS和MapReduce的属性
3. 我们可以用'Set' 命令去 为一个变量赋值，以及打印出变量值。
$hive --define foo=bar
hive> set foo;
foo=bar
hive> set hivevar:foo
> ;
hivevar:foo=bar
hive> set hivevar:foo=bar2;
hive> set foo;
foo=bar2
hive> set hivevar:foo;
hivevar:foo=bar2
hivevar: is one optional --hivevar and --define are same
hive> create table toss1(i int, ${hivevar:foo} string);
OK
Time taken: 7.339 seconds
hive> describe toss1;
OK
i int
bar2 string
Time taken: 1.773 seconds, Fetched: 2 row(s)
hive> create table toss2(i2 int, ${foo} string);
OK
Time taken: 0.769 seconds
hive> describe toss2;
OK
i2 int
bar2 string
Time taken: 0.463 seconds, Fetched: 2 row(s)
我们学习再学习下--hiveconf选项， Hive v0.7.*版本支持这个功能，其用于配置hive行为的所有属性。我们用它来指定Hive v0.8.0版本中增加的hive.cli.print.current.db属性。开启这个属性可以在CLI提示符打印当前所在的数据库名。默认为default.而且默认为false.
Let's learn --hiveconf optional, this function is surpported by Hive v0.7.*.
hive --hiveconf hive.cli.print.current.db=true
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/home/hadoop/apache-hive-2.1.0-bin/lib/log4j-slf4j-impl-2.4.1.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/home/hadoop/hadoop/share/hadoop/common/lib/slf4j-log4j12-1.7.10.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.apache.logging.slf4j.Log4jLoggerFactory]
Logging initialized using configuration in jar:file:/home/hadoop/apache-hive-2.1.0-bin/lib/hive-common-2.1.0.jar!/hive-log4j2.properties Async: true
Hive-on-MR is deprecated in Hive 2 and may not be available in the future versions. Consider using a different execution engine (i.e. spark, tez) or using Hive 1.X releases.
hive (default)> set hive.cli.print.current.db;
hive.cli.print.current.db=true
hive (default)> set hiveconf:hive.cli.print.current.db;
hiveconf:hive.cli.print.current.db=true
hive (default)> set hiveconf:hive.cli.print.current.db =false;
hive> set hiveconf:hive.cli.print.current.db;
hiveconf:hive.cli.print.current.db=false