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SQL Interview Success: Unlocking the Top 5 Frequently Asked Queries

 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

Messages in Kafka the Types and Details

A message, also called a record, is the basic piece of data flowing through Kafka. Messages are how Kafka represents your data.

types of messages

Kafka producer Vs. consumer messages

Kafka is an intermediate server that receives a message from a producer and sends them to the consumer. Here is a set of 10 Kafka Interview Questions.

Kafka message format

Each message has a timestamp, a value, and an optional key. Custom headers can be used if desired as well. 

A simple example of a message could be something like the following: the machine with host ID “1234567” (a message key) failed with the message “Alert: Machine Failed” (a message value) at “2020-10-02T10:34:11.654Z” (a message timestamp). Here is Kafka's flowchart for dummies.

Kafka message format
Kafka record

The above image shows probably the most important and common parts of a message that users deal with directly.

Each key and value can interact in its own specific ways to serialize or deserialize its data.

Now that we have a record, how do we let Kafka know about it? You will deliver this message to Kafka by sending it to what is known as brokers.



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