創(chuàng)建數(shù)據(jù)庫

CREATE DATABASE IF NOT EXISTS database_name;

查看所有數(shù)據(jù)庫

show databases

刪除數(shù)據(jù)庫

DROP DATABASE IF EXISTS sample_database;

進(jìn)入數(shù)據(jù)庫

use dbname

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創(chuàng)建表

CREATE TABLE IF NOT EXISTS test.student

(name STRING, age INT, contact INT );

查看所有表

show tables

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/指定HDFS路徑建庫

為了在HDFS文件系統(tǒng)中創(chuàng)建數(shù)據(jù)庫，需要指定要創(chuàng)建數(shù)據(jù)庫的位置，如下所示。

CREATE DATABASE IF NOT EXISTS database_name LOCATION hdfs_path;

實測會報無權(quán)限

CREATE DATABASE IF NOT EXISTS hdfstest LOCATION "/db/hdfstest";

改個有權(quán)限的目錄即可：

CREATE DATABASE IF NOT EXISTS hdfstest LOCATION "/user/impala/db/hdfstest";

注：通過hadoop fs -ls /user類似命令找到有權(quán)限的目錄

建表后會在hdfs數(shù)據(jù)庫目錄下創(chuàng)建表的目錄

插入數(shù)據(jù)后數(shù)據(jù)會存在表目錄中。

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insert

create table employee (Id INT, name STRING, age INT,address STRING, salary BIGINT);

insert into employee (ID,NAME,AGE,ADDRESS,SALARY)VALUES (1, 'Ramesh', 32, 'Ahmedabad', 20000 );

///查詢

select * from employee

排序

select id,name,age,address,salary from employee order by id

select * from employee order by salary desc nulls last

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select * from table_name ORDER BY col_name [ASC|DESC] [NULLS FIRST|NULLS LAST]

可以使用關(guān)鍵字ASC或DESC分別按升序或降序排列表中的數(shù)據(jù)。

以同樣的方式，如果我們使用NULLS FIRST，表中的所有空值都排列在頂行; 如果我們使用NULLS LAST，包含空值的行將最后排列。

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分組查詢

select name,sum(salary) from employee group by name

select name,sum(salary) from employee group by name having sum(salary)>20000

翻頁查詢

select * from employee order by id limit 2 offset 2

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///union

select * from employee order by id limit 2

union

select * from employee order by id limit 4

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select * from employee order by id limit 2

union all

select * from employee order by id limit 4

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with

with x as (select 1), y as (select 2) (select * from x union y);

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with t1 as (select * from employee where age>30),

t2 as (select * from employee where age>25)

(select * from t1 union all select * from t2);

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distinct

select distinct id,name from employee;

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/覆蓋插入（表的所有數(shù)據(jù)都被刪除）

Insert?overwrite?employee?values?(1,?'Ram',?26,??

'Vishakhapatnam',?37000?)?

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///獲取表的描述（表結(jié)構(gòu)）

describe employee

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改表名

ALTER TABLE [old_db_name.]old_table_name RENAME TO [new_db_name.]new_table_name

ALTER TABLE hdfstest.employee RENAME TO hdfstest.users;

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/添加列

ALTER TABLE users ADD COLUMNS (account_no BIGINT, phone_no BIGINT);

刪除列

ALTER TABLE users DROP account_no;

/更改列名和類型

ALTER TABLE users CHANGE phone_no e_mail string;

刪除表

drop table if exists my_db.student;

///清空表

truncate table_name;

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創(chuàng)建視圖

CREATE VIEW IF NOT EXISTS users_view AS

select name, age from users;

/修改視圖

alter view users_view AS

select name, age,e_mail from users;

//刪除視圖

drop view users_view

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參考鏈接：https://www.w3cschool.cn/impala/

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