How does Hive count the total number of entries in the entire database tables?

2 years ago
Liam
3 minutes

Hive can count the total number of entries in the entire database using two methods:

  1. One can utilize the built-in table and column statistics feature in Hive. The total number of entries in all tables within the database can be obtained by executing the following statement:
  2. Count all the records in the specified table from the specified database.
  3. This will return the total number of rows in the table, where is the name of the database and is the name of the table.
  4. Utilize the SHOW TABLES statement in Hive along with the DESCRIBE EXTENDED statement to count the number of entries in all tables in the database.
  5. First, execute the SHOW TABLES statement to obtain a list of all tables in the database. Then, use a loop to iterate through each table and execute the DESCRIBE EXTENDED statement to get detailed information about each table. Within this information, you can find the total number of rows in the table.
  6. Here is a sample script demonstrating how to use this method to count the number of entries in the entire database table.
  7. – Get a list of all tables in the database
    SHOW TABLES IN ;

    – Iterate through each table and retrieve detailed information
    SET hivevar:database_name=;
    SET hivevar:table_name=;

    – Set a variable to store the total row count
    SET hivevar:total_count=0;

    – Iterate through each table using a loop
    WHILE ${hivevar:table_name} IS NOT NULL
    DO
    – Retrieve detailed information about the table
    DESCRIBE EXTENDED ${hivevar:database_name}.${hivevar:table_name};

    – Extract the total row count of the table
    SET hivevar:count_query=SELECT COUNT(*) FROM ${hivevar:database_name}.${hivevar:table_name};
    INSERT OVERWRITE DIRECTORY ‘/tmp/hive_count’ ROW FORMAT DELIMITED FIELDS TERMINATED BY ‘\t’ ${hivevar:count_query};

    – Read the file storing the total row count of the table
    SET hivevar:count_file=`hadoop fs -cat /tmp/hive_count/*`;
    SET hivevar:count=`echo ${hivevar:count_file} | awk ‘{print $1}’`;

    – Accumulate the total row count
    SET hivevar:total_count=${hivevar:total_count}+${hivevar:count};

    – Get the name of the next table
    USE ${hivevar:database_name};
    SELECT ${hivevar:table_name} FROM (SELECT ${hivevar:table_name} FROM ${hivevar:database_name}. WHERE ${hivevar:table_name} > ‘${hivevar:table_name}’ ORDER BY ${hivevar:table_name} LIMIT 1) t INTO ${hivevar:table_name};

    END;

    – Print the total row count
    SELECT ${hivevar:total_count};

  8. Replace with the name of the database you want to analyze. This script will go through each table in the database and add up the total number of rows in each table. Finally, it will output the total number of rows.

Regardless of the method used, it is possible to count the number of entries in all tables in the Hive database as needed.

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