20 CRUD Interview Questions and Answers
Prepare for the types of questions you are likely to be asked when interviewing for a position where CRUD will be used.
CRUD is an acronym for “create, read, update, and delete”. These are the four basic functions that are typically performed on data in a database. When applying for a position that involves working with databases, you can expect to be asked questions about CRUD operations. In this article, we will review some of the most common CRUD interview questions and provide tips on how to answer them.
CRUD Interview Questions and Answers
Here are 20 commonly asked CRUD interview questions and answers to prepare you for your interview:
1. What is CRUD?
CRUD is an acronym for Create, Read, Update, and Delete. CRUD operations are the basic operations that can be performed on data in a database.
2. What are the four main operations performed in database systems?
The four main operations performed in database systems are known as CRUD: create, read, update, and delete. These operations are the basic functions that any database system must be able to perform in order to be useful.
3. Which operation is used to create a new entry in a database or table?
The operation used to create a new entry in a database or table is called the “create” operation. This operation is typically used when you are adding new data to a database.
4. How can you retrieve entries from a database using SQL?
You can use the SELECT statement to retrieve data from a database. The SELECT statement allows you to specify the columns that you want to retrieve data from, as well as the conditions that must be met in order for the data to be retrieved.
5. Can you explain how data is retrieved using a SELECT statement?
A SELECT statement is used to retrieve data from a database. The statement is written as a query, and the data is returned in a result set. The columns in the result set are determined by the columns that are listed in the SELECT statement. The data that is returned can be filtered using a WHERE clause, and the order of the data can be specified using an ORDER BY clause.
6. Are there any limitations when retrieving data with a SELECT statement?
Yes, there are a few limitations when retrieving data with a SELECT statement. One is that you can only select data from one table at a time. Another is that you can only select columns that you have permission to access. Finally, the ORDER BY clause can only be used to sort data in ascending or descending order; you cannot use it to sort data in any other way.
7. What does a WHERE clause do in an SQL query?
The WHERE clause is used to specify which records in a table should be returned by a query. The WHERE clause can be used to specify conditions based on column values, or to check if a value is null.
8. What’s the difference between % and * in SQL queries?
The percent sign (%) is a wildcard that matches any string of zero or more characters, while the asterisk (*) is a wildcard that matches any string of one or more characters. So, if you’re looking for all rows that contain the string “abc”, you would use:
SELECT * FROM table WHERE column LIKE ‘%abc%’
If you’re looking for all rows that start with “abc”, you would use:
SELECT * FROM table WHERE column LIKE ‘abc%’
9. How would you delete all records from a table called ‘users’?
To delete all records from a table called ‘users’, you would use the following SQL statement:
DELETE FROM users;
10. What is the usage of the DELETE FROM command?
The DELETE FROM command is used to delete data from a database table. The command will delete all data in the table that matches the specified criteria.
11. Is it possible to use conditions with the DELETE FROM statement? If yes, then how?
Yes, it is possible to use conditions with the DELETE FROM statement by using the WHERE clause. The WHERE clause allows you to specify which rows should be deleted and which should be left alone.
12. What is the best way to update existing records in a database?
The best way to update existing records in a database is to use the UPDATE statement. This statement allows you to modify the values of one or more columns in a table, and you can specify which rows to update by using a WHERE clause.
13. Can you explain how to update multiple columns with a single UPDATE statement?
Yes. When updating multiple columns, you need to specify only the columns that you want to update. For example, the following statement would update the “FirstName” and “LastName” columns:
UPDATE Customers
SET FirstName = ‘John’, LastName = ‘Smith’
WHERE CustomerID = 1
14. Why is it important to specify the condition while updating records?
It is important to specify the condition while updating records because it ensures that only the desired records are updated and that no other records are accidentally updated as well. This can help to avoid data loss or corruption.
15. What are some advantages of using CRUD?
CRUD allows for quick and easy data entry, retrieval, and manipulation. Additionally, CRUD can be used to enforce data integrity and security.
16. When should I use INSERT instead of REPLACE?
REPLACE is a MySQL extension to the SQL standard. It basically does a DELETE followed by an INSERT, but in one operation. So, if you are replacing an existing row in a table, it is more efficient to use REPLACE than to use two separate DELETE and INSERT operations.
17. What’s your opinion on the ON DUPLICATE KEY UPDATE option for MySQL databases?
I believe that the ON DUPLICATE KEY UPDATE option is a great way to ensure that data is always up-to-date in a MySQL database. This option allows you to specify what should happen if a row already exists with the same key value as the row you are trying to insert. This can be very useful in preventing data inconsistencies.
18. What are some disadvantages of CRUD?
CRUD can be very limiting because it only allows for the four basic operations to be performed on data. This can make it difficult to work with complex data sets or to perform more advanced operations. Additionally, CRUD can be very slow when working with large data sets because each operation has to be performed individually on each piece of data.
19. What does the acronym ACID stand for?
ACID stands for Atomic, Consistent, Isolation, and Durable. These are the four properties that are required for any database transaction to be considered valid. Atomic means that all of the operations in a transaction must be completed in order for the transaction to be considered successful. Consistent means that the transaction must leave the database in a consistent state. Isolation means that the transaction must be isolated from any other concurrent transactions. Durable means that the transaction must be durable, meaning that it will not be lost in the event of a system failure.
20. What process does the CREATE TABLE statement perform?
The CREATE TABLE statement is used to create a new table in a database. The statement will specify the name of the table, the name of the columns in the table, and the data type of each column. The CREATE TABLE statement will also specify any primary key or foreign key constraints that the table must adhere to.