![Q. How can insert & delete data from a table with SQL? Explain with example.
Insert: The main goal of database systems is to store data in the tables. The data is usually supplied
by application programs that run on top of the database. Towards that end, SQL has the INSERT
command that is used to store data into a table. The INSERT command creates a new row in the
table to store data.
INSERT INTO `table_name`(column_1,column_2,...) VALUES (value_1,value_2,...);
Delete command : The basic syntax of the delete command is as shown below.
DELETE FROM `table_name` [WHERE condition];
HERE
•DELETE FROM `table_name` tells MySQL server to remove rows from the table ..
•[WHERE condition] is optional and is used to put a filter that restricts the number of rows
affected by the DELETE query.
If the WHERE clause is not used in the DELETE query, then all the rows in a given table will
be deleted. Before we go into more details discussion the DELETE command, let's insert
some sample data into the movies table to work with.](https://image.slidesharecdn.com/pqs-1-200106082226/85/Islamic-University-Previous-Year-Question-Solution-2019-ADBMS-16-320.jpg)
Islamic University Previous Year Question Solution 2019 (ADBMS)
- 2. 1Q. What do you mean by DB? Discuss some applications of it. Ans: A database is a collection of information that is organized so that it can be easily accessed, managed and updated. Computer databases typically contain aggregations of data records or files, containing information about sales transactions or interactions with specific customers. Applications-
- 3. Q. Describe different levels of database user. Ans. Database users are the one who really use and take the benefits of database. 1. Application Programmers 2. Sophisticated Users 3. Specialized Users 4. Stand-alone Users 5. Native Users • Database Administrators - DBA can be a single person or it can be a group of person. Database Administrator is responsible for everything that is related to database. He makes the policies, strategies and provides technical supports. System Analyst - System analyst is responsible for the design, structure and properties of database. All the requirements of the end users are handled by system analyst. Feasibility, economic and technical aspects of DBMS is the main concern of system analyst.
- 4. Q. Describe the function of DBA. Database Administrator: One of the main reasons behind using DBMS is to have central control on both data and the applications access those data. The person who has such central control over the data is called a database administrator (DBA). Some of the functions of DBA are given below- • Five main functions of a database administrator are: • ·To create the scheme definition • ·To define the storage structure and access methods • ·To modify the scheme and/or physical organization when necessary • ·To grant authorization for data access • ·To specify integrity constraints
- 5. 2Q. Explain database instance and schema Definition of instance: The data stored in database at a particular moment of time is called instance of database. For example: In the following diagram, we have a schema that shows the relationship between three tables: Course, Student and Section. The diagram only shows the design of the database, it doesn’t show the data present in those tables. Schema is only a structural view(design) of a database as shown in the diagram below. Database schema defines the variable declarations in tables that belong to a particular database; the value of these variables at a moment of time is called the instance of that database. For example, lets say we have a single table student in the database, today the table has 100 records, so today the instance of the database has 100 records. Lets say we are going to add another 100 records in this table by tomorrow so the instance of database tomorrow will have 200 records in table. In short, at a particular moment the data stored in database is called the instance, that changes over time when we add or delete data from the database.
- 6. Q. Define entity set and relationship set. Ans. An entity set is a set of entities of the same type (e.g., all persons having an account at a bank). Entity sets need not be disjoint. For example, the entity set employee (all employees of a bank) and the entity set customer (all customers of the bank) may have members in common. Types of Entity Sets- • Strong entity set • Weak entity set A relationship set is a set of relationships of the same type. ... For example, consider the two entity sets customer and account. (Fig. 2.1 in the text). We define the relationship CustAcct to denote the association between customers and their accounts. Types of Relationship Sets- • Unary relationship set • Binary relationship set • Ternary relationship set • N-ary relationship se
- 7. Q. Describe database languages Database Language • A DBMS has appropriate languages and interfaces to express database queries and updates. • Database languages can be used to read, store and update the data in the database. 1. Data Definition Language • DDL stands for Data Definition Language. It is used to define database structure or pattern. • It is used to create schema, tables, indexes, constraints, etc. in the database. • Using the DDL statements, you can create the skeleton of the database. • Data definition language is used to store the information of metadata like the number of tables and schemas, their names, indexes, columns in each table, constraints, etc 2. DML stands for Data Manipulation Language. It is used for accessing and manipulating data in a database. It handles user requests. 3. Data Control Language • DCL stands for Data Control Language. It is used to retrieve the stored or saved data. • The DCL execution is transactional. It also has rollback parameters. 4. Transaction Control Language • TCL is used to run the changes made by the DML statement. TCL can be grouped into a logical transaction.
- 8. 3Q. Define super key and candidate key Super Key: Super Key is an attribute (or set of attributes) that is used to uniquely identifies all attributes in a relation. All super keys can’t be candidate keys but its reverse is true. In a relation, number of super keys are more than number of candidate keys. Candidate Key: Candidate key is a set of attributes (or attribute) which uniquely identify the tuples in a relation or table. As we know that Primary key is a minimal super key, so there is one and only one primary key in any relation but there is more than one candidate key can take place. Candidate key’s attributes can contain NULL value which oppose to the primary key.
- 9. Q. Explain mapping cardinality for binary relationship • Mapping cardinalities, or cardinality ratios, express the number of entities to which another entity can be associated via a relationship set. • Mapping cardinalities are most useful in describing binary relationship sets, although they can contribute to the description of relationship sets that involve more than two entity sets. • For a binary relationship set R between entity sets A and B, the mapping cardinality must be • One-to-one. An entity in A is associated with at most one entity in B, and an entity in B is associated with at most one entity in A • One-to-many. An entity in A is associated with any number (zero or more) of entities in B. An entity in B, however, can be associated with at most one entity in A • Many-to-one. An entity in A is associated with at most one entity in B. An entity in B, however, can be associated with any number (zero or more) of entities in A. • Many-to-many.An entity in A is associated with any number (zero or more) of entities in B, and an entity in B is associated with any number (zero or more) of entities in A.
- 10. Q. What do you mean by strong entity set & weak entity set? Explain with example. • Strong Entity: Strong entity is not dependent of any other entity in schema. Strong entity always has primary key. Strong entity is represented by single rectangle. Two strong entity’s relationship is represented by single diamond. Various strong entities together makes the strong entity set. • Weak Entity: Weak entity is depend on strong entity to ensure the existance of weak entity. Like strong entity weak entity does not have any primary key, It has partial discriminator key. Weak entity is represented by double rectangle. The relation between one strong and one weak entity is represented by double diamond.
- 11. 4Q. What is quarry language? Classify them. • Definition : Query language (QL) refers to any computer programming language that requests and retrieves data from database and information systems by sending queries. It works on user entered structured and formal programming command based queries to find and extract data from host databases. Query language may also be termed database query language. Query language is primarily created for creating, accessing and modifying data in and out from a database management system (DBMS). Typically, QL requires users to input a structured command that is similar and close to the English language querying construct. • For example, the SQL query: SELECT * FROM Classify • Thematic query: Selection of all objects which achieve the required conditions (attributes). E.g.: "Select all spruce trees." • Geometric query: Selection of all objects which achieve the required spatial conditions. E.g.: "Select all the houses that are located less than 250 m away from the river". • Topological query: Selection of all objects which achieve the required conditions regarding the spatial relations between the objects. For example: "Select all the buildings that are lying in zone 1".
- 12. Q. Explain fundamental operations of relational algebra Relational algebra is a widely used procedural query language. It collects instances of relations as input and gives occurrences of relations as output. It uses various operation to perform this action. Relational algebra operations are performed recursively on a relation. The output of these operations is a new relation, which might be formed from one or more input relations. Basic Relational Algebra Operations: 1. Unary Relational Operations 2. Relational Algebra Operations From Set Theory 3. Binary Relational Operations 4. SELECT (σ) 5. Projection(π) 6. Union operation (υ) 7. Intersection 8. Cartesian product(X) 9. Join Operations
- 13. Q. Explain Cartesian product operations of relational algebra The Cartesian Product is also an operator which works on two sets. It is sometimes called the CROSS PRODUCT or CROSS JOIN. It combines the tuples of one relation with all the tuples of the other relation.
- 14. 5Q. Describe different part of SQL language. SQL consists of three components: • Data Definition Language (DDL) • Data Manipulation Language (DML) • Data Control Language (DCL) The Data Definition Language (DDL). This component of the SQL language is used to create and modify tables and other objects in the database. For tables there are three main commands: • CREATE TABLE tablename to create a table in the database DROP TABLE tablename to remove a table from the database ALTER TABLE tablename to add or remove columns from a table in the database The Data Manipulation Language (DML) component of the SQL language is used to manipulate data within a table. There are four main commands: • SELECT to select rows of data from a table INSERT to insert rows of data into a table UPDATE to change rows of data in a table DELETE to remove rows of data from a table The Data Control Language (DCL) This component of the SQL language is used to create privileges to allow users access to, and manipulation of, the database. There are two main commands: • GRANT to grant a privilege to a user REVOKE to revoke (remove) a privilege from a user
- 15. Q. Explain the basic structure of SQL. A relational database is a collection of tables. Each table has its own unique name. The basic structure of an SQL expression consists of three clauses: • The select clause which corresponds to the projection operation. It is the list of attributes that will appear in the resulting table. • The from clause which corresponds to the Cartesian-product operation. It is the list of tables that will be joined in the resulting table. • The where clause which corresponds to the selection operation. It is the expression that controls the which rows appear in the resulting table. Example : select dept_name from instructor; where dept_name = ’Comp. Sci.’ and salary > 70000;
- 16. Q. How can insert & delete data from a table with SQL? Explain with example. Insert: The main goal of database systems is to store data in the tables. The data is usually supplied by application programs that run on top of the database. Towards that end, SQL has the INSERT command that is used to store data into a table. The INSERT command creates a new row in the table to store data. INSERT INTO `table_name`(column_1,column_2,...) VALUES (value_1,value_2,...); Delete command : The basic syntax of the delete command is as shown below. DELETE FROM `table_name` [WHERE condition]; HERE •DELETE FROM `table_name` tells MySQL server to remove rows from the table .. •[WHERE condition] is optional and is used to put a filter that restricts the number of rows affected by the DELETE query. If the WHERE clause is not used in the DELETE query, then all the rows in a given table will be deleted. Before we go into more details discussion the DELETE command, let's insert some sample data into the movies table to work with.
- 17. 6Q. What is domain constraints? Q. What is foreign key? Explain basic concept of it. Domain constraints can be defined as the definition of a valid set of values for an attribute. The data type of domain includes string, character, integer, time, date, currency, etc. The value of the attribute must be available in the corresponding domain. A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. The concept of referential integrity is derived from foreign key theory. Foreign keys and their implementation are more complex than primary keys. A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. It acts as a cross-reference between tables because it references the primary key of another table, thereby establishing a link between them.
- 18. Q. Define database trigger? Explain the trigger mechanism with an example. A database trigger is procedural code that is automatically executed in response to certain events on a particular table or view in a database. The trigger is mostly used for maintaining the integrity of the information on the database. A database trigger is special stored procedure that is run when specific actions occur within a database. Most triggers are defined to run when changes are made to a table's data. Triggers can be defined to run instead of or after DML (Data Manipulation Language) actions such as INSERT, UPDATE, and DELETE. • Example – Suppose, we are adding a tupple to the ‘Donors’ table that is some person has donated blood. So, we can design a trigger that will automatically add the value of donated blood to the ‘Blood_record’ table.
- 19. Continue Types of Triggers –We can define 6 types of triggers for each table: • AFTER INSERT activated after data is inserted into the table. • AFTER UPDATE: activated after data in the table is modified. • AFTER DELETE: activated after data is deleted/removed from the table. • BEFORE INSERT: activated before data is inserted into the table. • BEFORE UPDATE: activated before data in the table is modified. • BEFORE DELETE: activated before data is deleted/removed from the table.
- 20. 7Q. Define transaction? Q. Describe ACID properties. A transaction is a single logical unit of work which accesses and possibly modifies the contents of a database. Transactions access data using read and write operations. In order to maintain consistency in a database, before and after the transaction, certain properties are followed. These are called ACID properties.
- 21. Q. Explain different states of transaction deadlock & deadlock handling procedure Deadlock : Deadlock is a state of a database system having two or more transactions, when each transaction is waiting for a data item that is being locked by some other transaction. A deadlock can be indicated by a cycle in the wait-for-graph. This is a directed graph in which the vertices denote transactions and the edges denote waits for data items. • Example: • For example, in the following wait-for-graph, transaction T1 is waiting for data item X which is locked by T3. T3 is waiting for Y which is locked by T2 and T2 is waiting for Z which is locked by T1. Hence, a waiting cycle is formed, and none of the transactions can proceed executing.
- 22. Cont. •DEADLOCK HANDLING • When a deadlock occurs, different operating systems respond to them in different non- standard manners. • The Major approaches are as follows 1. IGNORING DEADLOCK 2. DETECTION
- 23. 8Q. Short note on (a) RAID level (b) Normalization (c) Sequential file organization • RAID stands for redundant array of independent disks. The technology combines two or more physical drives into a logical unit presented as a single hard drive to the operating system. Mirroring is duplicating data to more than one disk. It can speed read times because the system can read data from more than one disk. • Normalization is a database design technique which organizes tables in a manner that reduces redundancy and dependency of data. It divides larger tables to smaller tables and links them using relationships. Sequential file organization : A sequential file contains records organized by the order in which they were entered. The order of the records is fixed. Records in sequential files can be read or written only sequentially. After you place a record into a sequential file, you cannot shorten, lengthen, or delete the record. However, you can update (REWRITE) a record if the length does not change. New records are added at the end of the file. If the order in which you keep records in a file is not important, sequential organization is a good choice whether there are many