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SQL Interview Success: Unlocking the Top 5 Frequently Asked Queries

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 Here are the five top commonly asked SQL queries in the interviews. These you can expect in Data Analyst, or, Data Engineer interviews. Top SQL Queries for Interviews 01. Joins The commonly asked question pertains to providing two tables, determining the number of rows that will return on various join types, and the resultant. Table1 -------- id ---- 1 1 2 3 Table2 -------- id ---- 1 3 1 NULL Output ------- Inner join --------------- 5 rows will return The result will be: =============== 1  1 1   1 1   1 1    1 3    3 02. Substring and Concat Here, we need to write an SQL query to make the upper case of the first letter and the small case of the remaining letter. Table1 ------ ename ===== raJu venKat kRIshna Solution: ========== SELECT CONCAT(UPPER(SUBSTRING(name, 1, 1)), LOWER(SUBSTRING(name, 2))) AS capitalized_name FROM Table1; 03. Case statement SQL Query ========= SELECT Code1, Code2,      CASE         WHEN Code1 = 'A' AND Code2 = 'AA' THEN "A" | "A

How to Retain data in Kafka and Get Additional Time for Analysis

The default topic retention period in Kafka is seven days. However, you can change the current retention period and keep data for a few more days. Hence it provides you additional time for analysis to get business insights.


How to Retain data in Kafka and Get Additional Time for Analysis


Kafka retention period

  • The retention period, you can set on two parameters of bytes and time. Due to cheap storage costs, companies wish to extend the data retention period. 
  • The retention period setup you need in the broker. It is not a deviation that Kafka is designed only for Seven days, and why we need to change it. Since space is cheaper, we can extend the retention period.

Setup for the retention period

Below is the setup in the broker configuration file for the retention period.

log.retention.bytes


  • The most significant size threshold in bytes for deleting a log.


log.retention.ms

  • The length in milliseconds of a log will be maintained before being deleted.


log.retention.minutes


  • Length before deletion in minutes. log.retention.ms is used as well if both are set.


log.retention.hours

  • Length before deletion in hours. log.retention.ms and log.retention.minutes would be used before this value if both are set.

Steps to disable retention period

You can disable the retention period by setting both log.retention.bytes and log.retention.ms to –1. So that we can effectively turn off the data deletion.

Steps to store data outside the broker

If we want our data to stick around for a while, what is the option other than brokers?
  • Move the data outside of Kafka and not retain it internally to the Kafka brokers themselves. 
  • Before data is removed by retention from Kafka, we could store the data in a database, in a Hadoop Distributed File System (HDFS™), or upload our event messages into something like cloud storage.

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