What is the difference between SQL and PL/SQL?

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Answer:

SQL (Structured Query Language) and PL/SQL (Procedural Language/Structured Query Language) are both used in the context of managing and manipulating databases, but they serve different purposes and have distinct characteristics:

SQL (Structured Query Language):
- SQL is a domain-specific language primarily used for querying and manipulating relational databases.
- It is used to retrieve, insert, update, and delete data in a database.
- SQL statements are declarative in nature, meaning you specify what you want to do with the data, and the database management system (DBMS) figures out how to perform the operation.
- Common SQL commands include SELECT, INSERT, UPDATE, DELETE, JOIN, and GROUP BY.
PL/SQL (Procedural Language/Structured Query Language):
- PL/SQL is an extension of SQL that allows you to write procedural code within the database.
- It is used to create and manage programmatic constructs like stored procedures, functions, triggers, and packages within a database.
- PL/SQL enables you to write more complex logic, control structures (such as loops and conditionals), and error handling directly in the database.
- Unlike SQL, PL/SQL is a full programming language with procedural capabilities.
- PL/SQL programs are executed on the database server, reducing the need for data to be transferred between the client and the server.

In summary, SQL is primarily focused on data manipulation and retrieval, while PL/SQL extends SQL by adding procedural constructs for creating complex logic and operations that can be executed within the database itself. PL/SQL is particularly useful for building applications with business logic that needs to interact closely with the database, and it enhances the performance and security of database operations.

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808. How to delete a table in SQL Server?

Answer:

To delete a table in SQL Server, you can use the DROP TABLE statement. Make sure you have the necessary permissions to perform this action, as it will permanently remove the table and its data from the database. Here's the basic syntax:


DROP TABLE [schema_name.]table_name;

Replace schema_name with the name of the schema where the table resides (if applicable), and replace table_name with the name of the table you want to delete.

For example, to delete a table named "Employees" from the "dbo" schema:


DROP TABLE dbo.Employees;

If the table has any associated constraints, triggers, or indexes, you may need to drop those objects first before you can successfully delete the table. Be cautious when using this command, as data loss is irreversible.

Remember to take a backup of your database before performing any critical operations like dropping a table, especially in a production environment.

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809. How to update a database table using SQL?

Answer:

To update an existing Table we use SQL Command UPDATE: It will update the records as per user defined query/need.


Update TableName SET ColumnName = NewData where Condition   
Update info Set City = 'Baroda' where id = 2

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810. What is a database relationship?

Answer:

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811. What is a primary key of a database?

Answer:

Answer 1:

A table column with this constraint is called the key column for the table. This constraint helps the table to make sure that the value is not repeated and also that there are no null entries. This column does not allow null values and duplicate values. You can try inserting values to violate these conditions and see what happens. A table can have only one Primary key. Multiple columns can participate on the primary key.

Answer 2:

A primary key is a combination of fields which uniquely specify a row. This is a special kind of unique key, and it has implicit NOT NULL constraint. It means, Primary key values cannot be NULL.

A primary key in a database is a unique identifier for a record in a table. It serves two main purposes:

Uniqueness: A primary key ensures that each record in a table is uniquely identifiable. No two records in the table can have the same value for the primary key column(s). This uniqueness helps prevent data duplication and maintains data integrity.
Referential Integrity: A primary key is often used as a reference point for establishing relationships between tables in a relational database. It is used as a foreign key in related tables to create associations and maintain referential integrity. This ensures that data remains consistent across related tables.

Key characteristics of a primary key:

Uniqueness: Each value in the primary key column(s) must be unique across all records in the table.
Non-null: The primary key column(s) cannot contain null values. Every record must have a valid value in the primary key column(s).
Immutable: The values in the primary key column(s) should not change after the record is inserted into the table. This helps maintain the integrity of relationships and references.
Single or Composite: A primary key can consist of one or multiple columns, known as a composite primary key. In a composite primary key, the combination of values across the columns must be unique.

Example: Suppose you have a "Customers" table. You might designate the "CustomerID" column as the primary key. This ensures that each customer has a unique identifier, and you can use this identifier to establish relationships with other tables (e.g., orders, transactions) while maintaining data integrity.

SQL Syntax for creating a primary key:


CREATE TABLE Customers (
    CustomerID INT PRIMARY KEY,
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    LastName VARCHAR(50),
    Email VARCHAR(100)
);

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Answer:

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