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