How to create a table in SQL?

Long Question

522

Answer:

SQL provides an organized way for table creation:

Syntax

Create table TableName (columnName1 datatype, columnName2 datatype )

The following is an example of creating a simple table.

 create table Info   
(   
   Name varchar(20),   
   BirthDate date,   
   Phone nvarchar(12),   
   City varchar(20)   
)

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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.

# Tutorial: Delete or Drop table

Question: SQL Table Short

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

# Tutorial: Update Table

Question: SQL Table Short

810. What is a database relationship?

Answer:

Relationships are created by linking the column in one table with the column in another table. There are four different types of relationship that can be created.

The relationships are listed below:

One to One Relationship
Many to One relationship
Many to Many relationship
One to One relationship

# Tutorial: SQL Basic Overview

Question: SQL Introduction Short

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,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    Email VARCHAR(100)
);

In this example, the "CustomerID" column is defined as the primary key of the "Customers" table.

# Tutorial: Primary Key

Question: SQL Constraints Short

812. What is a foreign key of a database?

# Tutorial: Foreign Key

Question: SQL Constraints Long

813. What is database normalization?

# Tutorial: SQL Basic Overview

Question: SQL Introduction Long

814. What are database normalization forms?

Answer:

Normalization is the process of organizing data into a related table. it also eliminates redundancy and increases the integrity which improves performance of the query. To normalize a database, we divide the database into tables and establish relationships between the tables.

First Normal Form (1NF)
Second Normal Form (2NF)
Third Normal Form (3NF)
Boyce-Codd Normal Form (BCNF)
4th Normal Form
5th Normal Form
6th Normal Form

# Tutorial: SQL Basic Overview

Question: SQL Introduction Short

815. What is a stored procedure?

# Tutorial: Stored Procedures Introduction

Question: SQL Stored Procedures Long

816. What is a function in SQL Server?

# Tutorial: Functions Introduction

Question: SQL Functions Long

817. What is a join?

Answer:

This is a keyword used to query data from more tables based on the relationship between the fields of the tables. Keys play a major role when JOINs are used.

In SQL server, there are different types of JOINS.
1. CROSS JOIN
2. INNER JOIN
3. OUTER JOIN

Outer Joins are again divided into 3 types
1. Left Join or Left Outer Join
2. Right Join or Right Outer Join
3. Full Join or Full Outer Join

# Tutorial: Joins Introduction

Question: SQL Joins Short

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