, Dot Items
, Cargo Concat
, Employee Sales
, Employee Tree
, JSON Stock
, ATM Locations
, Ban Users
, Bank Branches
, Cheapest Product
, Department Report
, Employee Manager
, Hospital Patients
, Index Performance
, Menu Items
, Merge Stock Index
, Movies Live
, Restaurant Menu
, SMS Messages
, Student Activities
, Student Max Score
, Youngest Child
, Student Rankings
, Average Salary
, Welfare Organization
, Auto Show
, Movie Genres
, Manager Sales
SQL is the dominant technology for accessing application data. It is increasingly becoming a performance bottleneck when it comes to scalability. Given its dominance, SQL is a crucial skill for all engineers.
The delete statement is used to delete records in a table and is one of the four basic CRUD functions (create, read, update, and delete) required for working with any persistent storage.
Subqueries are commonly used in database interactions, making it important for a programmer to be skilled at writing them.
Conditional statements are a feature of most programming and query languages. They allow the programmer to control what computations are carried out based on a Boolean condition.
A database view is a result set that is defined by a stored query, the results of which can can also be queried. As a fundamental and widely used database construct, it's useful for candidates to understand how and when they should be used.
The UPDATE statement is used to modify the existing records in a table and is one of the most used operations for working with the database.
MySQL is an open-source relational database management system. It is one of the most widely used databases and is prominent in the popular LAMP stack.
String functions are used for manipulating, searching and processing strings. As almost all programs use strings, all developers should know how to make use of string functions.
An aggregate function is typically used in database queries to group together multiple rows to form a single value of meaningful data. A good programmer should be skilled at using data aggregation functions when interacting with databases.
Common table expression
Window functions operate on a set of rows and return a single value for each row from the underlying query. They are often useful since they does not suffer from information loss, unlike group by queries.
Common table expression
Common Table Expressions are used to simplify complex joins and recursive queries. It's a very useful tool for any developer who writes SQL.
JSON is an open-standard format that uses human-readable text to transmit data objects consisting of attribute-value pairs. It's the most common data format used for asynchronous browser/server communication.
Constraints are used to define rules and relationships. They are applied to a dataset. A constraint may take many forms, such as x ≤ 5 in a programming language and a NOT NULL constraint in a SQL table definition.
The CREATE TABLE statement is used to create a new table in a database. It is an essential command when creating new database.
A database schema defines how data is stored in a database. An SQL database uses a schema to define tables consisting of rows and columns that use fixed data types to store data. Formalizing how data is stored is the first step towards building an application or service.
The SELECT statement is used to select data from a database. It is the most used SQL command.
The CREATE INDEX statement is used to create indexes for tables. Indexes are used to retrieve data from the database more quickly. They are very important for making performant queries.
The performance of an application or system is important. The responsiveness and scalability of an application are all related to how performant an application is. Each algorithm and query can have a large positive or negative effect on the whole system.
The ALTER TABLE statement is used to add, delete, or modify columns and constraints in an existing table. Alter table statements are important for all programmers who have to modify existing schemas.
Knowing how to order data is a common task for every programmer.
Even though most database insert queries are simple, a good programmer should know how to handle more complicated situations like batch inserts.
LEFT JOIN is one of the ways to merge rows from two tables. We use it when we also want to show rows that exist in one table, but don't exist in the other table.
Everyone makes mistakes. A good programmer should be able to find and fix a bug in their or someone else's code.
The proper implementation and use of indexes are important for improving the performance of database queries.
The UNION operator is used to combine the result-set of two or more SELECT statements. It is often used when a report needs to be made based on multiple tables.
The GROUP BY statement groups rows by some attribute into summary rows. It is a common command when making various reports.
A normalized database is normally made up of multiple tables. Joins are, therefore, required to query across multiple tables.
The CASE statement is SQL's control statement. It goes through conditions and returns a value.
A CTE (Common Table Expression) is a temporary result set that can be referenced within another SELECT, INSERT, UPDATE, or DELETE statement. Recursive CTEs can reference themselves, which enables developers to work with hierarchical data.