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What is hive sql - hive commands ?

  • Commands are instructions, coded into SQL statements, which are used to communicate with the database to perform specific tasks, work, functions and queries with data. ...
  • These Data Manipulation Language commands are: SELECT, INSERT, UPDATE, and DELETE.
  • Start a Hive CLI(Command Line Interface) terminal and run
    --------$ hive
  • Should see a prompt like:
    --------hive>
  • Set a Hive or Hadoop conf prop:
    --------hive> set propkey=value;
  • List all properties and values:
    --------hive> set –v;
  • Add a resource to the DCache:
    --------hive> add [ARCHIVE|FILE|JAR] filename;
  • List tables:
    -------- hive> show tables;
  • Describe a table:
    -------- hive> describe <tablename>;
  • More information:
    -------- hive> describe extended <tablename>;
  • List Functions:
    -------- hive> show functions;
  • More information:
    -------- hive> describe function <functionname>;
  • Selecting data - Limiting top 10 data to display

    -------- hive> SELECT * FROM <tablename> LIMIT 10;
  • Selecting data - Top 10 data satisfying the where condition and sort by column
    -------- hive> SELECT * FROM <tablename> WHERE freq > 100 SORT BY freq ASC LIMIT 10;
  • Creating Tables in Hive
    -------- CREATE TABLE foo(id INT, msg STRING);
  • Changing Row Format
    -------- CREATE TABLE foo(id INT, msg STRING) DELIMITED FIELDS TERMINATED BY ‘,’ LINES TERMINATED BY ‘\n’;
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    Partitioning Data


    -------- CREATE TABLE foo (id INT, msg STRING)PARTITIONED BY (dt STRING);
  • Creates a subdirectory for each value of the partition column, e.g.:
    -------- /user/hive/warehouse/foo/dt=2009-03-20/
  • -------- Queries with partition columns in WHERE clause will scan through only a subset of the data

    DML OPERATIONS

    Examples:
  • Loads a file that contains two columns separated by ctr-a into wikitechy table. 'LOCAL' signifies that the input is on the local file system.
  • If 'LOCAL' is omitted then it looks for the file in HDFS. The keyword 'OVERWRITE' signifies that existing data in the table is deleted.
  • If the 'OVERWRITE' keyword is omitted, data files are appended to existing data sets.

  • --------hive> LOAD DATA LOCAL INPATH './examples/files/kv1.txt'
    --------hive> OVERWRITE INTO TABLE wikitechy;

  • The two LOAD statements below load data into two different partitions of the table invites.
  • Table invites must be created as partitioned by the key ds for this to succeed.

  • --------hive> LOAD DATA LOCAL INPATH './examples/files/kv2.txt' OVERWRITE INTO TABLE invite PARTITION (ds='2008-08-15');
    --------hive> LOAD DATA LOCAL INPATH './examples/files/kv3.txt' OVERWRITE INTO TABLE invites PARTITION (ds='2008-08-08');

  • The below command will load data from an HDFS file/directory to the table.
  • Note that loading data from HDFS will result in moving the file/directory.

  • --------hive> LOAD DATA INPATH '/user/myname/kv2.txt';
    --------hive>OVERWRITE INTO TABLE invites PARTITION (ds='2008-08-15');

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    Hive Commands

    • Hive supports Data definition Language(DDL), Data Manipulation Language(DML) and User defined functions.

    Hive DDL Commands

    • create database
    • drop database
    • create table
    • drop table
    • Truncate table
    • alter table
    • create index
    • create views

    Create Database in Hive

    • DDL command in Hive is used for creating databases.
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    Syntax

    CREATE (DATABASE) [IF NOT EXISTS] database_name
    
      [COMMENT database_comment]
    
      [LOCATION hdfs_path]
    
      [WITH DBPROPERTIES (property_name=property_value, ...)];
    
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    • In the above syntax for create database command, the values mentioned in square brackets [] are optional.

    Drop Database in Hive

    • This command is used for deleting an already created database in Hive.
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    Syntax

    DROP (DATABASE) [IF EXISTS] database_name [RESTRICT|CASCADE];
    
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    Alter Database Command in Hive

    • The developers want to change the metadata of any of the databases, can be used alter hive DDL command.
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    Syntax

    ALTER (DATABASE) database_name SET DBPROPERTIES (property_name=property_value, ...);
    
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    DDL Commands on Tables in Hive

    Create Table Command in Hive

    • Hive create table command is used to create a table in the existing database that is in use for a particular session.
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    Syntax

    CREATE  TABLE [IF NOT EXISTS] [db_name.]table_name    --
    
      [(col_name data_type [COMMENT col_comment], ...)]
    
      [COMMENT table_comment]
    
       [LOCATION hdfs_path]
    
    
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    DROP Table Command in Hive

    • Drops the table and all the data associated with it in the Hive metastore.

    Syntax

    DROP TABLE [IF EXISTS] table_name [PURGE];
    
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    TRUNCATE Table Command in Hive

    • This hive command is used to truncate all the rows present in a table.
    • It is deletes all the data from the Hive meta store and the data cannot be restored.
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    Syntax

    TRUNCATE TABLE [db_name].table_name
    
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    ALTER Table Command in Hive

    • To use ALTER Table command, the structure and metadata of the table can be modified even after the table has been created.
    • Let us try to change the name of an existing table using the ALTER command

    Syntax

    ALTER TABLE [db_name].old_table_name RENAME TO [db_name].new_table_name;
    
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    Hive DML Commands

    • DML (Data Manipulation Language) commands in Hive are used for inserting and querying the data from hive tables once the structure and architecture of the database has been defined using the DDL commands.
      • Select
      • Where
      • Group By
      • Order By
      • Load Data
      • Join
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    SELECT Table command in Hive

    • · Let check whether the data has been loaded correctly by selecting the rows from Student_name.

    Example

    hive> select * from Student_name;
    
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    Where Table command in Hive

    • A WHERE clause is used to filter the result set by using predicate operators and logical operators.
    • Functions can also be used to compute the condition.
      • List of Predicate Operators
      • List of Logical Operators
      • List of Functions

    Example

    hive> SELECT name FROM table_name WHERE name = 'xxxxx';
    
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    GROUP BY

    • Contrast this to the GROUP BY clause, which is used to group like column values into a single row.
    • This is useful as it allows you to summarize information.
    • For example you can use aggregate functions such as SUM and AVERAGE to calculate values.

    Example

    SELECT   SalesOrderID,
             SUM(OrderQty* UnitPrice) As TotalPrice
    FROM     Sales.SalesOrderDetail
    GROUP BY SalesOrderID
    
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    ORDER BY

    • The ORDER BY statement is used to sort values.

    Example

    SELECT   SalesOrderID,
             ProductID,
             OrderQty* UnitPrice As ExtendedPrice
    FROM     Sales.SalesOrderDetail
    ORDER BY SalesOrderID
    
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    • It will sort the value, according to SalesOrderID.
    • Every row in the table is included in the result. The values are sorted in ascending order according to the SalesOrderID.
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    LOAD DATA Statement

    • The LOAD DATA statement streamlines the ETL process for an internal Impala table by moving a data file or all the data files in a directory from an HDFS location into the Impala data directory for that table.

    Syntax:

    LOAD DATA INPATH 'hdfs_file_or_directory_path' [OVERWRITE] INTO TABLE tablename
      [PARTITION (partcol1=val1, partcol2=val2 ...)]
    
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    • When the LOAD DATA statement operates on a partitioned table, it always operates on one partition at a time.
    • Require the PARTITION clauses and list all the partition key columns, with a constant value specified for each.
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    Hive Special Commands

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    Hive Shell Commands

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