Hive 教程(三)-DDL基础

DDL，Hive Data Definition Language，数据定义语言；就是数据库那一套，本文总结一下基本方法

管理表 vs 外建表

管理表也称内建表；hive 默认创建的表都是管理表；

管理表和外建表的数据都存储在 hdfs，因为都是 hive 的表；

区别

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

如果创建外部表，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；

在实际工作中，一般使用外建表

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 的地址并不是 hive 默认的 hdfs 地址，说明是可以指定非默认地址的

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 无法更改

可能只有 Hive 2.2.1, 2.4.0 and later 才可以，我的是 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

显示所有数据库名称

show databases;

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]

后面还有很多参数，具体可参照官网 - 下面的参考资料

参数解释

temporary：

exeternal：创建一个外部表，同时需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，如果原数据的格式不符，可以写入表，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，自己写的不能用，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

　　// 如果是纯文本文件，可以用 stored as textfile；如果是压缩文件，可以用 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

示例

hive> create table student(id int,name string) row format delimited fields terminated by '\t'; 创建表，以
hive> create  table if not exists student1 like student; 创建一个和表一样模式的表

hive> create table if not exists mytable(sid int,sname string)
    >  row format delimited fields terminated by '\005' 
    >  stored as textfile; 创建内部表
    
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'; 创建外部表
    
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;    创建分区表

测试 row format 

写入如下数据到 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)

可以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

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

增加或者替换列

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";

还有很多，请查看官网

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