What Are Databases and Tables in SQL?
Introduction
Data Science is the extraction of knowledge or meaningful insights via thorough examination and analysis of data. We must first extract the information from the database to examine it. This is where SQL comes into the picture, making it the most in-demand data-related programming language.
Relational Database Management is an essential component of Data Science. A database has one or more tables that can be characterized as relational tables. In SQL databases, tables serve as the fundamental organizing structure. They comprise multiple columns that indicate the unique characteristics of each row, or record, in the SQL table. It’s vital for everyone who deals with relational databases to comprehend how to create, alter, and remove tables.
In this article, you will learn about SQL databases and SQL tables in databases.
What Is a Table in SQL?
Tables are the foundation of every database system, and they can hold more than 30 different types of data. It offers a systematic method of storing data to keep your database structured.
SQL Table is a database object that holds the information in a database. A table in SQL logically arranges data in a row-and-column structure comparable to spreadsheets. Each row represents a distinct record, and each column represents a record field.
Records and Fields in SQL
Tables comprise rows and columns, with rows referred to as records and columns referred to as fields.
A column is a collection of data values of a certain type (such as integers or alphanumeric characters), one entry for each row of the database, such as Gender, Student Roll number, or Student Name.
A row in a table refers to a single data item; every row has the same layout, such as Shane[Student_name] or 007[Student_Roll number].
Fields in SQL
Fields are columns in a table containing specific data details.
Consider the table below; the table contains a SALARY field that includes information on the salaries of several employees. Similarly, the age column contains information on various employees’ ages.
| EMP_NAME | Emp_age | Department | SALARY |
| Ann | 35 | HR | 15000 |
| Ben | 40 | Sales | 18000 |
| Shane | 29 | Marketing | 20000 |
Records in SQL
A record is simply a single entry in a table. Records include all of the information about a particular entry or entity. Consider the table below. Shane is chosen from one of the rows. This row contains detailed information about the employee, Shane.
| EMP_NAME | Emp_age | Department | SALARY |
| Ann | 35 | HR | 15000 |
| Ben | 40 | Sales | 18000 |
| Shane | 29 | Marketing | 20000 |
Databases in SQL
In SQL Server, a database is made of a set of tables that store a certain collection of structured data. An SQL database table containing payroll information for a business may include a row for each staff and columns including personnel records such as employee number, name, department, address, salary information, contact number, and joining date.
- The number of tables in a database is entirely determined by the number of objects that can be stored in it. A basic user-defined table can have up to 1,024 columns. The server data storage capacity entirely determines the number of rows in the table.
- You can manage the allowed data and other attributes by assigning attributes to the table and each column in the SQL table. For example, you can set requirements on a column to prevent null values, offer a default value if no value is given, or attach a key constraint to the table to ensure uniqueness or establish a connection between tables.
- The content in the SQL table can be compressed by row or page. Data compression allows for more rows to integrate on a page.
Types of Tables in database
SQL tables are classified into the following sections:
System Tables
SQL Server contains instance setup and database attributes in a separate collection of system tables. Users are not authorized to make direct modifications to these tables. SQL Server does not permit direct queries on certain system tables. Instead, it supports probing these elements using system-stored processes, functions, Replication Management Objects, and SQL Server Management Objects.
Temporary Tables
We may need to temporarily store data in the database for computation, modification, or saving interim results. In such instances, we may use the temporary tables, which are stored in the TempDB system database.
There are two main types of temporary tables in SQL Server:
- Local: Each local temporary table begins with a symbol (#). It only applies to the current connection. When the user disconnects, SQL Server automatically deletes these tables.
- Global: Each global temporary table begins with a symbol (##). The global temporary tables are accessible to all users. SQL Server removes the global table if all users who are querying it are connected.
Permanent or User-defined table
Users can customize their table structure, columns, data types, criteria, and indexes to meet the needs of their applications. These are known as user-defined tables.
Unless specifically dropped, these tables are always kept in the database. As a result, these are commonly referred to as permanent tables.
In SQL Server, there are several methods for creating a user-defined SQL database table.
- SQL Server Management Studio GUI
- Using T-SQL script
External Tables
These are a subtype of the table that can be utilized starting with SQL Server 2016. Using SQL Server’s PolyBase functionality, these tables correspond to various data sources such as Hadoop, Azure blob storage, Oracle, Excel, MongoDB, ODBC, Bigdata, and Teradata.
Graph Tables
SQL Server graph databases use many nodes and edges.
- Node table: The node table is a set of nodes with similar types. For instance, The person node table contains all the person nodes in a graph.
- Edge table:The edge table is a set of similar edges. For instance, An acquaintance table contains all edges that connect one person to another.
SQL Table Syntax and Example
Let’s learn how to work with tables in SQL with the help of examples.
Create a Table in SQL
The ‘create table’ DDL command is used to create a table in a SQL database. Let’s look at how to make a table in SQL.
Syntax:
Create Table
To build a SQL table, follow the given steps.
CREATE TABLE table_Name(Column_Name1 data_type size)
A table column must have a name, a data type, and a data type size.
Example:
To create a table in SQL.
CREATE TABLE Student(ID INT(12));
CREATE TABLE customer(ID INT(15));
The first statement creates a table named student with a field ID of type int length 10. Similarly, the second command creates a table named customer with a column ID of type int.
In this manner, we can build a table in the SQL database.
Alter Table
The Alter table command is used to change the layout of an existing table. For example, we can simply execute the following operation using the alter table:
- Insert a new column into the existing table.
- Change the table’s name.
- Removing the column from the present table.
These are some of the most common operations we can carry out using the alter table command. Let’s look at some instances to comprehend these operations better.
Adding a column to the present table.
Using the Alter table command, we can add a new column to the table. Let’s go through the syntax for introducing a new column.
Syntax:
ALTER TABLE table_Name add column_Name data_type;
Rename the Table
The Alter table command can be used to rename the table. Let’s look at the syntax for renaming the table.
Syntax:
ALTER TABLE last__table_name RENAME new__table_name;
Deleting the column from the existing table.
The syntax for removing a specific column from a table is shown below.
Syntax:
ALTER TABLE Student
DROP COLUMN Roll_no;
Delete Table
We have two options for deleting the table:
- Delete all of the SQL table’s records without deleting the table structure.
- Delete all records as well as the table structure.
Let’s go through both methods and the commands that are needed to carry them out.
- Delete all of the SQL table’s records without deleting the table structure:
The Delete command is a Data manipulation language command that is used to remove all the records in a table while keeping the database’s structure. We can also use the where clause to remove a specific table entry.
Let’s have a look at how to delete a SQL table.
Syntax:
DELETE FROM Table_Name;
The syntax above is used to remove all records while maintaining the table’s layout.
Example:
Table_Name: Student_record
| Admission_number | Name | Marks_scored | Class |
| 101 | Aaran | 10 | 5 |
| 102 | Ben | 15 | 5 |
| 103 | Keya | 12 | 6 |
Using the Select command select the table Student Record
SELECT * FROM student_record;
The command above will display all of the table’s records. Let’s look at how to delete a SQL table using the delete command.
Deleting the table student record
DELETE FROM student_record;
Selecting the Student record table
After selecting the table student, we obtain a blank table.
- Delete all records as well as the SQL database table layout.
The DROP command deletes all records and the structure of the table.
Let’s look at the syntax for deleting a SQL table using the drop command.
Syntax:
DROP TABLE table__name;
This syntax is used to remove all of the records as well as the table’s structure. This is similar to the delete command, except it does not keep the table’s layout.
Truncate Table
This truncate SQL database table command is used to erase all the records from the table without removing the table structure, but it does not accept the where clause.
Let’s comprehend the syntax of the truncate command in the SQL table.
Syntax:
TRUNCATE TABLE table_Name;
The given syntax of the truncate in the SQL table is utilized to remove the records from the table.
SELECT * FROM student_record;
The command above will display all of the table’s records. Using the truncate command, let’s look at how to truncate a SQL table.
Truncating Student Record table
TRUNCATE Student_record;
The information in the student record table is removed after truncating it, but the layout will remain unchanged.
Difference Between Truncate and Delete Command
| Truncate | Delete |
| Truncate is a Data Definition Language command. | Delete command is a Data Manipulation language command. |
| The Where clause is not acceptable to be used in the truncate command. | The Where clause can be used in the Delete command. |
| The record cannot be deleted using the Truncate command. | The Delete command can delete the specified SQL table records. |
| The truncate command takes less time to execute. | The Delete command takes longer to execute than the Truncate command. |
Conclusion
SQL expertise is an essential and practical skill big tech companies are looking for. Learning SQL tables assists in a broad range of operations in SQL databases. In fact, Data Scientists must have sound knowledge of SQL to perform their duties aptly.
Now that you understand what SQL database table is, it’s time for you to start practicing and get the expertise to access and interpret the vast amount of data. For professional-grade knowledge and IIM Indore certification, UNext’s PG Certificate Program in Data Science and Machine Learning is best suited for you.
