Hive 教程(三)-DDL基础

DDL，Hive Data Definition Language，数据定义语言；

通俗理解就是数据库与库表相关的操做，本文总结一下基本方法

 

hive 数据仓库配置

hive 数据仓库默认位置在 hdfs 上的 /user/hive/warehouse 路径下；

hive 有个默认的数据库叫 default；

可是在 /user/hive/warehouse 路径下没有建立 default 文件夹，default 下的表是直接在 /user/hive/warehouse 路径下 建立文件夹

 

在 hive 中，数据库对应 hdfs 上一个路径（叫文件夹或者更合适），数据表也对应 hdfs 上一个路径，数据对应 hdfs 上一个文件

 

管理表 vs 外建表

管理表也称内建表；hive 默认建立的表都是管理表；

管理表和外建表的数据都存储在 hdfs，由于都是 hive 的表；

 

区别

hive 在建立内部表时，会把数据移动到数据仓库指定的路径，如 hdfs 某个地方；

若是建立外部表，不会移动数据，仅在元数据中记录数据所在的位置；

最大的区别在于：当删除内部表时，同时删除数据和元数据；当删除外部表时，仅删除元数据，不删除数据；

 

鉴于这种特性，管理表不适合共享数据，容易产生安全问题；

在实际工做中，通常使用外建表

 

相互转换

查看表的类型

hive> desc formatted student_p;
Table Type:             MANAGED_TABLE 

管理表 to 外部表

hive> alter table student_p set tblproperties('EXTERNAL'='TRUE');
Table Type:             EXTERNAL_TABLE  

外部表 to 管理表

hive> alter table student_p set tblproperties('EXTERNAL'='FALSE');

注意必须大写

 

Database

Create Database

CREATE (DATABASE|SCHEMA) [IF NOT EXISTS] database_name
  [COMMENT database_comment]
  [LOCATION hdfs_path]
  [WITH DBPROPERTIES (property_name=property_value, ...)];

示例

hive> create database hive1101 location '/usr/hive_test';
OK
Time taken: 0.12 seconds

注意这里 location 的地址并非 hive 默认的 hdfs 地址，说明是能够指定非默认地址的

 

Drop Database

数据库必须是空的

DROP (DATABASE|SCHEMA) [IF EXISTS] database_name [RESTRICT|CASCADE];

 

Alter Database

改变数据库的属性

ALTER (DATABASE|SCHEMA) database_name SET DBPROPERTIES (property_name=property_value, ...);   -- (Note: SCHEMA added in Hive 0.14.0)
ALTER (DATABASE|SCHEMA) database_name SET OWNER [USER|ROLE] user_or_role;   -- (Note: Hive 0.13.0 and later; SCHEMA added in Hive 0.14.0)
ALTER (DATABASE|SCHEMA) database_name SET LOCATION hdfs_path; -- (Note: Hive 2.2.1, 2.4.0 and later)

示例

hive> alter database hive1101 set dbproperties ('edit_by'='wjd');
OK
Time taken: 0.118 seconds

注意，location 没法更改

可能只有 Hive 2.2.1, 2.4.0 and later 才能够，个人是 2.3.6，没有测试

 

Use Database

切换到目标数据库下

USE database_name;
USE DEFAULT;

 

Show Database

显示全部数据库名称

show databases;

 

显示数据库信息

hive> desc database hive1101;
OK
hive1101        hdfs://hadoop10:9000/usr/hive_test    root    USER    
Time taken: 0.182 seconds, Fetched: 1 row(s)

只显示了元数据信息，也能够 在 database 后加 extended，能多显示一些信息

 

Table

Create Table

CREATE [TEMPORARY] [EXTERNAL] TABLE [IF NOT EXISTS] [db_name.]table_name    -- (Note: TEMPORARY available in Hive 0.14.0 and later)
  [(col_name data_type [column_constraint_specification] [COMMENT col_comment], ... [constraint_specification])]
  [COMMENT table_comment]
  [PARTITIONED BY (col_name data_type [COMMENT col_comment], ...)]
  [CLUSTERED BY (col_name, col_name, ...) [SORTED BY (col_name [ASC|DESC], ...)] INTO num_buckets BUCKETS]
  [SKEWED BY (col_name, col_name, ...)                  -- (Note: Available in Hive 0.10.0 and later)]
     ON ((col_value, col_value, ...), (col_value, col_value, ...), ...)
     [STORED AS DIRECTORIES]
  [
   [ROW FORMAT row_format] 
   [STORED AS file_format]
     | STORED BY 'storage.handler.class.name' [WITH SERDEPROPERTIES (...)]  -- (Note: Available in Hive 0.6.0 and later)
  ]
  [LOCATION hdfs_path]

后面还有不少参数，具体可参照官网 - 下面的参考资料

 

参数解释

temporary：

exeternal：建立一个外部表，同时须要指定实际数据所在的路径，location 来指定

like：复制表结构，但不复制数据

row format：指定每行的格式，若是原数据的格式不符，能够写入表，但不能正确的写入表

　　// delimited fields terminated by '\t'  　以 \t 为间隔

　　// delimited fields terminated by ','　　注意逗号分隔的只能是 csv 文件，本身写的不能用，会出错

　　// delimited 间隔；terminated 结尾；

ROW FORMAT 
DELIMITED [FIELDS TERMINATED BY char] [COLLECTION ITEMS TERMINATED BY char] 
    [MAP KEYS TERMINATED BY char] [LINES TERMINATED BY char] 
   | SERDE serde_name [WITH SERDEPROPERTIES (property_name=property_value, property_name=property_value, ...)]

stored as： 加载的文件格式

　　// 若是是纯文本文件，能够用 stored as textfile；若是是压缩文件，能够用 stored as  SEQUENCEFILE

　　// 还有 ORC、json 等多种个数，可查看官网

partitioned by：分区表，这个很重要，后面专门讲

CLUSTERED BY：分桶表，后面和分区表一块儿将

 

示例

hive> create table student(id int,name string) row format delimited fields terminated by '\t'; 建立表，以
hive> create  table if not exists student1 like student; 建立一个和表同样模式的表

hive> create table if not exists mytable(sid int,sname string)
    >  row format delimited fields terminated by '\005' 
    >  stored as textfile; 建立内部表
    
hive> create external table if not exists pageview(
    >  pageid int,
    >  page_url string comment 'the page url'
    > )
    > row format delimited fields terminated by ','
    > location 'hdfs://192.168.220.144:9000/user/hive/warehouse'; 建立外部表
    
hive> create table student_p(id int,name string,sexex string,age int,dept string)
    >  partitioned by(part string)
    >  row format delimited fields terminated by ','
    >  stored as textfile;    建立分区表

 

测试 row format 

写入以下数据到 student，以 \t 为间隔

1    a
2    b
3    c
4 d,

很显然，最后一行不是以 \t 间隔

hive> load data local inpath '/usr/lib/hive2.3.6/1.txt' into table student;
Loading data to table hive1101.student
OK
Time taken: 0.868 seconds
hive> select * from student;
OK
1    a
2    b
3    c
NULL    NULL
Time taken: 0.17 seconds, Fetched: 4 row(s)

能够看到最后一行没有正确的写入

 

Drop Table

DROP TABLE [IF EXISTS] table_name [PURGE];     -- (Note: PURGE available in Hive 0.14.0 and later)

 

Truncate Table

清空表；注意不能清空外部表

TRUNCATE TABLE table_name [PARTITION partition_spec];
 
partition_spec:
  : (partition_column = partition_col_value, partition_column = partition_col_value, ...)

 

Alter Table

修改表的属性

 

Rename Table

ALTER TABLE table_name RENAME TO new_table_name;

 

Alter Table Properties

ALTER TABLE table_name SET TBLPROPERTIES table_properties;
 
table_properties:
  : (property_name = property_value, property_name = property_value, ... )

 

Alter Table Comment

ALTER TABLE table_name SET TBLPROPERTIES ('comment' = new_comment);

 

Add SerDe Properties

ALTER TABLE table_name [PARTITION partition_spec] SET SERDE serde_class_name [WITH SERDEPROPERTIES serde_properties];
 
ALTER TABLE table_name [PARTITION partition_spec] SET SERDEPROPERTIES serde_properties;
 
serde_properties:
  : (property_name = property_value, property_name = property_value, ... )

 

Alter Column

Change Column Name/Type/Position/Comment

修改列的名字，类型，位置 等

ALTER TABLE table_name [PARTITION partition_spec] CHANGE [COLUMN] col_old_name col_new_name column_type
  [COMMENT col_comment] [FIRST|AFTER column_name] [CASCADE|RESTRICT];

示例

CREATE TABLE test_change (a int, b int, c int);
 
// First change column a's name to a1.
ALTER TABLE test_change CHANGE a a1 INT;
 
// Next change column a1's name to a2, its data type to string, and put it after column b.
ALTER TABLE test_change CHANGE a1 a2 STRING AFTER b;
// The new table's structure is:  b int, a2 string, c int.
  
// Then change column c's name to c1, and put it as the first column.
ALTER TABLE test_change CHANGE c c1 INT FIRST;
// The new table's structure is:  c1 int, b int, a2 string.
  
// Add a comment to column a1
ALTER TABLE test_change CHANGE a1 a1 INT COMMENT 'this is column a1';

 

Add/Replace Columns

增长或者替换列

ALTER TABLE table_name 
  [PARTITION partition_spec]                 -- (Note: Hive 0.14.0 and later)
  ADD|REPLACE COLUMNS (col_name data_type [COMMENT col_comment], ...)
  [CASCADE|RESTRICT]                         -- (Note: Hive 1.1.0 and later)

 

Index

Create Index

CREATE INDEX index_name
  ON TABLE base_table_name (col_name, ...)
  AS index_type
  [WITH DEFERRED REBUILD]
  [IDXPROPERTIES (property_name=property_value, ...)]
  [IN TABLE index_table_name]
  [
     [ ROW FORMAT ...] STORED AS ...
     | STORED BY ...
  ]
  [LOCATION hdfs_path]
  [TBLPROPERTIES (...)]
  [COMMENT "index comment"];

 

Drop Index

DROP INDEX [IF EXISTS] index_name ON table_name;

 

Alter Index

ALTER INDEX index_name ON table_name [PARTITION partition_spec] REBUILD;

 

Show

Show Databases

SHOW (DATABASES|SCHEMAS) [LIKE 'identifier_with_wildcards'];

 

Show Tables

SHOW TABLES [IN database_name] ['identifier_with_wildcards'];

 

Show Table Properties

SHOW TBLPROPERTIES tblname;
SHOW TBLPROPERTIES tblname("foo");

 

Show Create Table

SHOW CREATE TABLE ([db_name.]table_name|view_name);

 

Show Indexes

SHOW [FORMATTED] (INDEX|INDEXES) ON table_with_index [(FROM|IN) db_name];

 

Show Columns

SHOW COLUMNS (FROM|IN) table_name [(FROM|IN) db_name];

示例

-- SHOW COLUMNS
CREATE DATABASE test_db;
USE test_db;
CREATE TABLE foo(col1 INT, col2 INT, col3 INT, cola INT, colb INT, colc INT, a INT, b INT, c INT);
  
-- SHOW COLUMNS basic syntax
SHOW COLUMNS FROM foo;                            -- show all column in foo
SHOW COLUMNS FROM foo "*";                        -- show all column in foo
SHOW COLUMNS IN foo "col*";                       -- show columns in foo starting with "col"                 OUTPUT col1,col2,col3,cola,colb,colc
SHOW COLUMNS FROM foo '*c';                       -- show columns in foo ending with "c"                     OUTPUT c,colc
SHOW COLUMNS FROM foo LIKE "col1|cola";           -- show columns in foo either col1 or cola                 OUTPUT col1,cola
SHOW COLUMNS FROM foo FROM test_db LIKE 'col*';   -- show columns in foo starting with "col"                 OUTPUT col1,col2,col3,cola,colb,colc
SHOW COLUMNS IN foo IN test_db LIKE 'col*';       -- show columns in foo starting with "col" (FROM/IN same)  OUTPUT col1,col2,col3,cola,colb,colc
  
-- Non existing column pattern resulting in no match
SHOW COLUMNS IN foo "nomatch*";
SHOW COLUMNS IN foo "col+";                       -- + wildcard not supported
SHOW COLUMNS IN foo "nomatch";

 

加载数据

不属于 DDL，属于 DML，后面会讲

 

 

参考资料：

https://cwiki.apache.org/confluence/display/Hive/LanguageManual+DDL　　官网

https://ask.hellobi.com/blog/wujiadong/9483

https://blog.csdn.net/xiaozelulu/article/details/81585867