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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
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4 Upcoming New Protocols in Internet-of-things

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4 Upcoming New Protocols in Internet-of-things
#4 Upcoming New Protocols in Internet-of-things:
4 New Protocols recently discussed in IoT conference:
  • 6LoWPAN for embedded device networking
  • The Constrained Access Protocol (CoAP) for low-power device communication.
  • The Time Synchronized Mesh Protocol (TSMP) for saving power in environments with limited wireless bandwidth.
  • RPL, the IPv6 Routing Protocol for Low power and Lossy Networks, for defining and changing routes among devices.
Another downside is the lack of Quality of Service (QoS). Making sure that messages are delivered is even more important in the IoT world than it was in the instant messaging world. If your alarm system doesn’t receive the message to turn itself on, then that vacation you’ve been planning could easily be ruined.

 What is CoAP
CoAP is a simple request/response protocol (again, very similar to REST) that follows a traditional client/server model. Clients can make GET, PUT, POST, and DELETE requests to resources. CoAP packets use bitfields to maximize memory efficiency, and they make extensive usage of mappings from strings to integers to keep the data packets small enough to transport and interpret on-device. Aside from the extremely small packet size, another major advantage of CoAP is its usage of UDP; using datagrams allows for CoAP to be run on top of packet-based technologies like SMS.

One of the downsides of CoAP: It's a one-to-one protocol. Though extensions that make group broadcasts possible are available, broadcast capabilities are not inherent to the protocol. Arguably, an even more important disadvantage is the lack of a publish-subscribe message queue.

The major advantages of MQTT are the publish-subscribe message queue and the many-to-many broadcast capabilities. Using a long-lived outgoing TCP connection to the MQTT broker, sending messages of limited bandwidth back and forth is simple and straightforward. 

The downside of having an always-on connection is that it limits the amount of time the devices can be put to sleep. If the device mostly sleeps, then another MQTT protocol can be used: MQTT-S, which works with UDP instead of TCP.

Another disadvantage of MQTT is the lack of encryption in the base protocol. MQTT was designed to be a lightweight protocol, and incorporating encryption would add a significant amount of overhead to the connection. You can add custom security at the application level, but that may require a significant amount of work.

What is XMPP
The primary advantage is XMPP's decentralized nature. XMPP works similar to email, operating across a distributed network of transfer agents rather than relying on a single, central server or broker (as CoAP and MQTT do). As with email, it’s easy for anyone to run their own XMPP server, allowing device manufacturers and API operators to create and manage their own network of devices. And because anyone can run their own server, if security is required, that server could be isolated on a company intranet behind secure authentication protocols using built-in TLS encryption. 

 Unfortunately, there are a few disadvantages to XMPP as well. One of the largest flaws is the lack of end-to-end encryption. While there are many use cases in which encryption may not yet be necessary, most IoT devices will ultimately need it. The lack of end-to-end encryption is a major downside for IoT manufacturers.

All CoAP messages can be marked as either “confirmable” or “nonconfirmable,” serving as an application-level QoS. While SSL/TLS encryption isn’t available over UDP, CoAP makes use of Datagram Transport Layer Security (DTLS), which is analogous to the TCP version of TLS. The default level of encryption is equivalent to a 3,072-bit RSA key. Even with all of this, CoAP is designed to work on microcontrollers with as little as 10KB of RAM.

3 Real time Protocols currently using:
XMPP Protocol -The eXtensible Messaging and Presence Protocol (XMPP) is a TCP communications protocol based on XML that enables near-real-time exchange of structured data between two or more connected entities. Out-of-the-box features of XMPP include presence information and contact list maintenance. While both features were originally designed for instant messaging, they have obvious applications for IoT. Due in part to its open nature and XML foundation, XMPP has been extended for use in publish-subscribe systems -- again, perfect for IoT applications. There are several major advantages to using XMPP as your IoT communications protocol.

 CoAP Protocol -The Constrained Application Protocol (CoAP) was specifically developed to allow resource-constrained devices to communicate over the Internet using UDP instead of TCP. Developers can interact with any CoAP-enabled device the same way they would with a device using a traditional REST-based API. CoAP is particularly useful for communicating with low-power sensors and devices that need to be controlled via the Internet. 

 MQTT Protocol -Message Queue Telemetry Transport (MQTT) is a publish-subscribe messaging protocol. Similar to CoAP, it was built with resource-constrained devices in mind. MQTT has a lightweight packet structure designed to conserve both memory usage and power. A connected device subscribes to a topic hosted on an MQTT broker. Every time another device or service publishes data to a topic, all of the devices subscribed to it will automatically get the updated information. 

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