MariaDB Interview Questions and Answers

When we use a NULL value, it means they are unknown values. We can not consider them as empty strings or zero, which are valid values. In table creation, section details take into consideration setting them to acknowledge null values, or reject them. Essentially use a NULL or NOT NULL statement. This has applications in instances of missing record data like an ID number. Client characterized factors have an estimation of NULL until express task. Put away routine parameters and neighborhood factors permit setting an estimation of NULL. At the point when a neighborhood variable has no default esteem, it has an estimation of NULL.

There are certain operators cannot use with Null operator as result will be null also. Standard comparison operators cannot compare null values because it will return only null, not true or false.

Other available forms of operators are −

• IS NULL − It gives you result after testing for a NULL value.
• IS NOT NULL − It gives you confirmation about the unavailability of a NULL value.
• ISNULL − If it discovery a NULL value it returns a value of 1 if it is absent it returns a value of 0.
• COALESCE − In case of absence it returns a NULL value but generally, returns the first non-NULL value of a list.

As we know, JOIN retrieves data from the various table.

There are three forms of JOIN-

1) INNER JOIN : is the most common method of JOIN in which user get row from multiple tables when join condition is satisfied.

2) LEFT OUTER JOIN : This method returns all row from the left-hand table when ON condition is satisfied.

3) RIGHT OUTER JOIN : This method returns all row from the left-hand table when ON condition is satisfied.

A regular expression used to match string on a given pattern. String match pattern use for search option.

A transaction is a sequence of various operations. They work individually but terminates only when each operation executes successfully. Which mean once all operations have been completed only then the transaction will be successful. In case of a single operation gets fail it impacts the entire transaction as each sequence depends up to another one.

The general structure of an exchange explanation comprises of starting with START TRANSACTION. The subsequent stage is embeddings at least one or more commands/operations, inserting statements that check for mistakes, inserting ROLLBACK statements to deal with any error found, at last, inserting a COMMIT statement to implement modification on a successful operation.

• Atomicity − It interrupts the failures and rolls back the modification because It is responsible accomplish all operations.
• Consistency − It is responsible for changes implement by the database on a successful transaction.
• Isolation − It prepares the transaction operations to perform individually in a transaction.
• Durability − It is responsible for the persistence of a successful transaction in case an event of system failure occurs.

Alter command innovate the structure of an existing table, which allows modification such as add and remove of columns, modification of indices, modification in data types and modification in names. At the point metadata lock is active, Alter command is ready to apply modifications.

Indexes are tools to retrieve records by acceleration. An index column gets an entry for each value by an index production. Indexes are a companion with the various column, assist quick exploration and sufficient record management. Creating an index is consider which columns are frequently using in your query.

MariaDB uses indexes intensely to optimize queries given quick access to data and gave statistics. There are some users found indexes are complicated to manage. MariaDB provides a self-sufficient storage engine along with the availability of statistics table. Statistics are calculated by storage engine for every table in every storage engine. storage engine even calculates the statistics for columns that are not indexed.