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For any stored data if we want to preserve the consistency and correctness, a relational DBMS typically imposes one or more data integrity constraints. These constraints restrict the data values which can be inserted into the database or created by a database update.Data Integrity ConstraintsThere are different types of data integrity constraints that are commonly found in relational databases, including the following −Required data − Some columns in a database contain a valid data value in each row; they are not allowed to contain NULL values. In the sample database, every order has an associated customer who placed the order. ... Read More
Cash book records all the transactions related to cash in an organization. Transactions are recorded according to their type (debit or credit). These are recorded in chronological order. Cash book can be both a journal and a ledgerFeatures of cash bookThe features of cash book are explained below −Act as both journal and ledger − Cash books records transactions as it happens and posts the transactions.Substitution − It serves as an alternative for cash accounts.Dual entry − Cash book has two sides namely, debit side and credit side.Identical − Debit side (total) = credit side (total).Debit balance − Business will ... Read More
Let us first try to understand why we are using B-tree. Then, we will get a clarity on the definition of B-tree.Reasons for using B-treeThe reasons for using B-tree are as follows −When searching tables on disc, the cost of accessing the disk is high but it doesn’t bother about the amount of data transferred. So our aim is to minimize disc access.We know that we cannot improve the height of trees. So, we wish to make the height of the tree as small as possible.The solution for this is to use a B-tree, it has more branches and thus ... Read More
The advantages and disadvantages of some of the collision resolution techniques are explained below −Separate Chaining hashingSeparate chaining is a hashing technique in which there is a list to handle collisions. So there are many elements at the same position and they are in a list. The sequences are maintained in a linked list.The advantages of separate chaining hashing are as follows −Separate chaining technique is not sensitive to the size of the table.The idea and the implementation are simple.The disadvantages of separate chaining hashing are as follows −Keys are not evenly distributed in separate chaining.Separate chaining can lead to ... Read More
Collision is a problem that occurs when two keys applied on a hash table map to the same location in the hash table.There are two techniques that are used to avoid collision they are −Linear probing.Chaining.Let us discuss each technique in detail.Linear probingLinear probing is a strategy for resolving collisions. In this the new key is placed in the closest following empty cell.Here the elements are stored wherever the hash function maps into a hash table, if that cell is filled then the next consecutive location is searched to store that value. Here generally we use arrays.Step 1 − Let ... Read More
Hashed file organisation is also called a direct file organisation.In this method, for storing the records a hash function is calculated, which provides the address of the block to store the record. Any type of mathematical function can be used as a hash function. It can be simple or complex.Hash function is applied to columns or attributes to get the block address. The records are stored randomly. So, it is also known as Direct or Random file organization.If the generated hash function is on the column which is considered as key, then the column can be called as hash key ... Read More
Different organizations have struggled with their management information systems and their membership databases. The main struggle here is the lack of centralized information. Too often, assurance and non-profits keep separate databases for membership, events, sales, and other processes. When at all feasible, these databases should be combined into a single, centralized database.Advantages of centralized database over other databasesThe advantages of centralized database over other databases are explained below −Data integrity − In a centralized database the data integrity is maximized and data redundancy is minimized, as the single storing place of all the data also implies that a given set ... Read More
A distributed database is the one where all the storage devices are not attached to a common CPU (central processing unit). It may be distributed over a network of interconnected computers, or it may be stored in multiple computers located in the same physical location.Distributed Database Management SystemA distributed database management system (DDBMS) manages the database as in if it is stored in the same computer.The DDBMS synchronizes all the data in a periodical manner and in situations when multiple users are accessing the same data and ensures that updation and deletion performed on the data at one location shall ... Read More
A Clustered index is one of the special types of index which reorders the way records in the table are physically stored on the disk. It sorts and stores the data rows in the table or view based on their key values. It is essentially a sorted copy of the data in the indexed columns.Sometimes we are asked to create an index on a non-unique key like dept-id in the below table. There could be several employees in each department. Here, all employees belonging to the same dept-id are considered to be within a single cluster, and the index pointers ... Read More
In the primary index there is a one-to-one relationship between the entries in the index table and records in the main table. Primary index is used on a primary key.Types of Primary IndexPrimary index are of two types, which are as follows −Dense Primary IndexIn a dense primary index an index record appears for every search key value in the main table that means each and every record in the main table has an entry in the index.ExampleGiven below is an example of dense primary index −A pointer stores the address of a record.Non-Dense / Sparse Primary indexAn index record ... Read More