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- SQL Interview Questions and Answers
- SQL Server Interview Questions for 2-5 Years Experienced [UPDATED 2021]
- 100+ Most Popular SQL Interview Questions And Answers
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SQL Interview Questions and Answers
UNION merges the contents of two structurally-compatible tables into a single combined table. So, in cases where is is certain that there will not be any duplicates, or where having duplicates is not a problem, use of UNION ALL would be recommended for performance reasons. This is the default type of join if no specific JOIN type is specified. Explain your answer and also provide an alternative version of this query that will avoid the issue that it exposes.
Surprisingly, given the sample data provided, the result of this query will be an empty set. It will always be true since ID is not a member of dbo. As such, it will refer to the envelope table comparing itself to itself!
Although there are 4 customers not referred by Jane Smith including Jane Smith herself , the query will only return one: Pat Richards. This will return the same faulty set as the original.
Those particular operators will always evaluate to true or false. Considering the database schema displayed in the SQLServer-style diagram below, write a SQL query to return a list of all the invoices. The list should be ordered by billing date. There is nothing tricky in this one, it just covers the basics:.
If not, any invoices by customers not referred by somebody will be left out altogether. Did the candidate alias the tables in the JOIN? Most experienced T-SQL programmers always do this, because repeating the full table name each time it needs to be referenced gets tedious quickly.
Again, this is something most experienced programmers do automatically, whether or not there would be a conflict. And again, in this case there would be a conflict, so the query would break if the candidate neglected to do so. Note that this query will not return Invoices that do not have an associated Customer. This may be the correct behavior for most cases e. If there are 10 records in the Emp table and 5 records in the Dept table, how many rows will be displayed in the result of the following SQL query:.
In Oracle, the minus keyword is used instead. MySQL does not support the except function. Given a table TBL with a field Nmbr that has rows with the following values:. Write a SQL query to find the 10th highest employee salary from an Employee table. Explain your answer. However, those salaries will be listed in descending order.
That was necessary for the first query to work, but now picking the top 1 from that list will give you the highest salary not the the 10th highest salary.
Therefore, the second query reorders the 10 records in ascending order which the default sort order and then selects the top record which will now be the lowest of those 10 salaries. Not all databases support the TOP keyword. Why might you want to do this? The key is the AND a! Write a query to to get the list of users who took the a training lesson more than once in the same day, grouped by user and training lesson, each ordered from the most recent lesson date to oldest date.
Execution plans are very useful for helping a developer understand and analyze the performance characteristics of a query or stored procedure, since the plan is used to execute the query or stored procedure. If this option is turned on, it will display query execution plans in a separate window when a query is run.
List and explain each of the ACID properties that collectively guarantee that database transactions are processed reliably. ACID Atomicity, Consistency, Isolation, Durability is a set of properties that guarantee that database transactions are processed reliably. They are defined as follows:. Given a table dbo. With the NVL exp1, exp2 function, if exp1 is not null, then the value of exp1 is returned; otherwise, the value of exp2 is returned, but case to the same data type as that of exp1.
With the NVL2 exp1, exp2, exp3 function, if exp1 is not null, then exp2 is returned; otherwise, the value of exp3 is returned. Provide an example. Write a single SQL statement to concatenate all the customer names into the following single semicolon-separated string:. This is close, but will have an undesired trailing ;. One way of fixing that could be:. When stored in a database, varchar2 uses only the allocated space.
But when stored in a database, char always uses the maximum length and is blank-padded. Now the client wants to insert a record after the identity value 7 with its identity value starting from Imagine a single column in a table that is populated with either a single digit or a single character a-z, A-Z. This will give the third-highest salary from the Employee table. Write a single query to calculate the sum of all positive values of x and he sum of all negative values of x.
What would be a better way to write it? Id, i. BillingDate, c. Name, r. Given a table TBL with a field Nmbr that has rows with the following values: 1, 0, 0, 1, 1, 1, 1, 0, 0, 1, 0, 1, 0, 1, 0, 1 Write a query to add 2 where Nmbr is 0 and add 3 where Nmbr is 1.
Note: You may assume that there are at least 10 records in the Employee table. What is an execution plan? When would you use it?
How would you view the execution plan? They are defined as follows: Atomicity. An atomic system must guarantee atomicity in each and every situation, including power failures, errors, and crashes.
The consistency property ensures that any transaction will bring the database from one valid state to another. Any data written to the database must be valid according to all defined rules, including constraints, cascades, triggers, and any combination thereof.
The isolation property ensures that the concurrent execution of transactions results in a system state that would be obtained if transactions were executed serially, i. Providing isolation is the main goal of concurrency control. Depending on concurrency control method i.
Durability means that once a transaction has been committed, it will remain so, even in the event of power loss, crashes, or errors. In a relational database, for instance, once a group of SQL statements execute, the results need to be stored permanently even if the database crashes immediately thereafter. To defend against power loss, transactions or their effects must be recorded in a non-volatile memory.
How can you select all the even number records from a table? All the odd number records? How do they differ? The filtering occurs before any groupings are made. What will be the output of the below query, given an Employee table having 10 records?
What is the difference between single-row functions and multiple-row functions? What is the group by clause used for? Single-row functions work with single row at a time.
Multiple-row functions work with data of multiple rows at a time. The group by clause combines all those records that have identical values in a particular field or any group of fields. What is the difference between char and varchar2? Can we insert a row for identity column implicitly? How do you get the last id without the max function? Suppose in a table, seven records are there. The column is an identity column. Is it possible?
If so, how? If not, why not? How can you use a CTE to return the fifth highest or Nth highest salary from a table? Given the following table named A : x 2 -2 4 -4 -3 0 2 Write a single query to calculate the sum of all positive values of x and he sum of all negative values of x.
Consider the Employee table below. How do you copy data from one table to another table? How to find a duplicate record? At the end of the day, hiring remains an art, a science — and a lot of work. Submit a Question. Thanks for submitting your question. Our editorial staff will review it shortly. Design your career as a SQL developer with Toptal.
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SQL Server Interview Questions for 2-5 Years Experienced [UPDATED 2021]
A database is a collection of information in an organized form for faster and better access, storage, and manipulation. It can also be defined as a collection of tables, schema, views, and other database objects. Data warehouse refers to a central repository of data from multiple sources of information. Those data are consolidated, transformed and made available for the mining as well as online processing. A table is a database object used to store records in a field in the form of columns and rows that holds data.
UNION merges the contents of two structurally-compatible tables into a single combined table. So, in cases where is is certain that there will not be any duplicates, or where having duplicates is not a problem, use of UNION ALL would be recommended for performance reasons. This is the default type of join if no specific JOIN type is specified. Explain your answer and also provide an alternative version of this query that will avoid the issue that it exposes. Surprisingly, given the sample data provided, the result of this query will be an empty set. It will always be true since ID is not a member of dbo.
What is Failover clustering overview? Answer: Failover clustering is mainly used for data availability. Typically, in a failover cluster, there are two machines. One machine provides the basic services and the second is available to run the service when the primary system fails. The primary system is monitored periodically to check if it works. This monitoring may be performed by the failover computer or an independent system also called a cluster controller.
100+ Most Popular SQL Interview Questions And Answers
Best possible SQL questions that could boost your confidence for your next Database Developer job interview. Well, there are more, but this distilled set of questions covers all SQL functionalities, which will enable you to get better prepared to face an interview. Here we have listed top SQL interview questions and answers that are frequently asked by the interviewer. Answer: DBMSs are software applications that help you build and maintain databases. Answer: A join is used to query data from multiple tables based on the relationship between the fields.
A database is an organized collection of data, stored and retrieved digitally from a remote or local computer system. Databases can be vast and complex, and such databases are developed using fixed design and modeling approaches. DBMS is a system software responsible for the creation, retrieval, updation and management of the database. It ensures that our data is consistent, organized and is easily accessible by serving as an interface between the database and its end users or application softwares. The key difference here, compared to DBMS, is that RDBMS stores data in the form of a collection of tables and relations can be defined between the common fields of these tables.
SQL programming skills are highly desirable and required in the market, as there is a massive use of Database Management Systems DBMS in almost every software application. In order to get a job, candidates need to crack the interview in which they are asked various SQL interview questions. Following is a curated list of SQL interview questions and answers, which are likely to be asked during the SQL interview. Candidates are likely to be asked basic SQL interview questions to advance level SQL questions depending on their experience and various other factors. The below list covers all the SQL interview questions for freshers as well as SQL interview questions for experienced level candidates and some SQL query interview questions.
PRIME DIFFERENCE BETWEEN ELEMENTS RESPONSIBLE FOR HIROSHIMA AND NAGASAKI ГЛАВНАЯ РАЗНИЦА МЕЖДУ ЭЛЕМЕНТАМИ, ОТВЕТСТВЕННЫМИ ЗА ХИРОСИМУ И НАГАСАКИ - Это даже не вопрос! - крикнул Бринкерхофф. - Какой же может быть ответ. - Нам необходимо число, - напомнил Джабба. - Шифр-убийца имеет цифровую структуру. - Тихо, - потребовал Фонтейн и повернулся к Сьюзан.
Она знала, что, пока ТРАНСТЕКСТ будет продолжать сжирать аварийное питание, она останется запертой в Третьем узле. Стратмор отпустил створки двери, и тонюсенькая полоска света исчезла. Сьюзан смотрела, как фигура Стратмора растворяется во тьме шифровалки. ГЛАВА 63 Новообретенная веспа Дэвида Беккера преодолевала последние метры до Aeropuerto de Sevilla.
- Я там. У него случился инфаркт. Я сам. Никакой крови. Никакой пули.
Стратмор нетвердыми шагами двинулся к дрожащему корпусу и упал на колени, как грешник перед лицом рассерженного божества. Все предпринятые им меры оказались бесполезными. Где-то в самом низу шахты воспламенились процессоры. ГЛАВА 105 Огненный шар, рвущийся наверх сквозь миллионы силиконовых чипов, производил ни на что не похожий звук.
У нас нет времени, чтобы… - Никакая служба здесь не появится, Сьюзан. У нас столько времени, сколько. Сьюзан отказывалась понимать. Не появится. - Но вы же позвонили… Стратмор позволил себе наконец засмеяться.
Сьюзан пробежала мимо них с одной только мыслью - как можно скорее предупредить Стратмора. Сотрудник лаборатории систем безопасности схватил ее за руку. - Мисс Флетчер.