What are the basic SQL queries asked in interview?

What are the basic SQL queries asked in interview?

SQL Interview Questions

• What is Database? A database is an organized collection of data, stored and retrieved digitally from a remote or local computer system.
• What is DBMS?
• What is RDBMS?
• What is SQL?
• What is the difference between SQL and MySQL?
• What are Tables and Fields?
• What are Constraints in SQL?

What are the SQL queries asked in interview for freshers?

SQL Query Interview Questions for Freshers

• Write an SQL query to fetch the EmpId and FullName of all the employees working under Manager with id – ‘986’.
• Write an SQL query to fetch the different projects available from the EmployeeSalary table.
• Write an SQL query to fetch the count of employees working in project ‘P1’.

Where can I practice SQL queries for interview?

SQLPad gives you everything you need to succeed in a SQL interview. Watch, learn and practice data interview coding questions all in your browser. Every question thoughtfully designed in a business context. One-stop-shop to improve your data skills to a whole new level.

How do I prepare for SQL interview?

Six-step strategy for your SQL interview

1. Restate the question to make sure you understand what you’re being asked to do.
2. Explore the data by asking questions.
3. Identify the columns you’ll need to solve the problem.
4. Think about what your answer should look like.
5. Write your code one step at a time.

What are the 5 basic SQL commands?

Some of The Most Important SQL Commands

• SELECT – extracts data from a database.
• UPDATE – updates data in a database.
• DELETE – deletes data from a database.
• INSERT INTO – inserts new data into a database.
• CREATE DATABASE – creates a new database.
• ALTER DATABASE – modifies a database.
• CREATE TABLE – creates a new table.

How do you delete duplicates in SQL?

1) First identify the rows those satisfy the definition of duplicate and insert them into temp table, say #tableAll . 2) Select non-duplicate(single-rows) or distinct rows into temp table say #tableUnique. 3) Delete from source table joining #tableAll to delete the duplicates.

How do I find duplicates in SQL?

How to Find Duplicate Values in SQL

1. Using the GROUP BY clause to group all rows by the target column(s) – i.e. the column(s) you want to check for duplicate values on.
2. Using the COUNT function in the HAVING clause to check if any of the groups have more than 1 entry; those would be the duplicate values.

What is the primary key in SQL?

In SQL, a primary key is a single field or combination of fields that uniquely defines a record. None of the fields that are part of the primary key can contain a NULL value. A table can have only one primary key. You use either the CREATE TABLE statement or the ALTER TABLE statement to create a primary key in SQL.

How do I select the last 5 records of a SQL table?

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1. You need to count number of rows inside table ( say we have 12 rows )
2. then subtract 5 rows from them ( we are now in 7 )
3. select * where index_column > 7 select * from users where user_id > ( (select COUNT(*) from users) – 5) you can order them ASC or DESC.

What is the index in SQL?

An index contains keys built from one or more columns in the table or view. These keys are stored in a structure (B-tree) that enables SQL Server to find the row or rows associated with the key values quickly and efficiently.

How do you delete duplicate records in Oracle?

To delete duplicate records in Oracle, start by making sure the records are actually duplicates by entering the Standard Query Language, or SQL. After entering “SQL,” search for what you want to delete, like “delete from names where name = ‘Alan. ‘” Then, enter “commit” for this command to take effect.

How can I delete duplicate records?

Remove duplicate values

1. Select the range of cells that has duplicate values you want to remove. Tip: Remove any outlines or subtotals from your data before trying to remove duplicates.
2. Click Data > Remove Duplicates, and then Under Columns, check or uncheck the columns where you want to remove the duplicates.
3. Click OK.

Can primary key be null?

A primary key defines the set of columns that uniquely identifies rows in a table. When you create a primary key constraint, none of the columns included in the primary key can have NULL constraints; that is, they must not permit NULL values.

Can foreign key be null?

A foreign key containing null values cannot match the values of a parent key, since a parent key by definition can have no null values. However, a null foreign key value is always valid, regardless of the value of any of its non-null parts.

IS NULL check in SQL?

Description. The IS NULL condition is used in SQL to test for a NULL value. It returns TRUE if a NULL value is found, otherwise it returns FALSE. It can be used in a SELECT, INSERT, UPDATE, or DELETE statement.

What is the primary key?

A primary key, also called a primary keyword, is a key in a relational database that is unique for each record. It is a unique identifier, such as a driver license number, telephone number (including area code), or vehicle identification number (VIN). A relational database must always have one and only one primary key.

What is Pragma Autonomous_transaction?

The AUTONOMOUS_TRANSACTION pragma changes the way a subprogram works within a transaction. A subprogram marked with this pragma can do SQL operations and commit or roll back those operations, without committing or rolling back the data in the main transaction.

What are Joins in Oracle?

A join is a query that combines rows from two or more tables, views, or materialized views. Oracle Database performs a join whenever multiple tables appear in the FROM clause of the query. The select list of the query can select any columns from any of these tables.

How do you select data without duplicates in SQL?

If you want the query to return only unique rows, use the keyword DISTINCT after SELECT . DISTINCT can be used to fetch unique rows from one or more columns. You need to list the columns after the DISTINCT keyword.

How do I filter duplicate records in SQL?

Using the GROUP BY clause to group all rows by the target column(s) – i.e. the column(s) you want to check for duplicate values on. Using the COUNT function in the HAVING clause to check if any of the groups have more than 1 entry; those would be the duplicate values.
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RESULT.

What is a unique key in SQL?

A unique key is a set of one or more than one fields/columns of a table that uniquely identify a record in a database table. You can say that it is little like primary key but it can accept only one null value and it cannot have duplicate values.

Can primary key be duplicated?

You can define keys which allow duplicate values. However, do not allow duplicates on primary keys as the value of a record’s primary key must be unique. When you use duplicate keys, be aware that there is a limit on the number of times you can specify the same value for an individual key.

Can foreign key be duplicate?

Short answer: Yes, it can be NULL or duplicate. I want to explain why a foreign key might need to be null or might need to be unique or not unique. First remember a Foreign key simply requires that the value in that field must exist first in a different table (the parent table).

What is NVL () in SQL?

NVL(expr1, expr2) : In SQL, NVL() converts a null value to an actual value. Data types that can be used are date, character and number.

How do you DELETE duplicates in SQL?