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SQL Table

  • SQL Table is a collection of data which is organized in terms of rows and columns. In DBMS, the table is known as relation and row as a tuple.
  • Table is a simple form of data storage. A table is also considered as a convenient representation of relations.

Let's see an example of the EMPLOYEE table:

EMP_ID EMP_NAME CITY PHONE_NO
1 Kristen Washington 7289201223
2 Anna Franklin 9378282882
3 Jackson Bristol 9264783838
4 Kellan California 7254728346
5 Ashley Hawaii 9638482678

In the above table, "EMPLOYEE" is the table name, "EMP_ID", "EMP_NAME", "CITY", "PHONE_NO" are the column names. The combination of data of multiple columns forms a row, e.g., 1, "Kristen", "Washington" and 7289201223 are the data of one row.

Operation on Table

  1. Create table
  2. Drop table
  3. Delete table
  4. Rename table

SQL Create Table

SQL create table is used to create a table in the database. To define the table, you should define the name of the table and also define its columns and column's data type.

Syntax

Example

If you create the table successfully, you can verify the table by looking at the message by the SQL server. Else you can use DESC command as follows:

SQL> DESC EMPLOYEE;

Field Type Null Key Default Extra
EMP_ID int(11) NO PRI NULL
EMP_NAME varchar(25) NO NULL
PHONE_NO NO int(11) NULL
ADDRESS YES NULL char(30)
  • 4 rows in set (0.35 sec)

Now you have an EMPLOYEE table in the database, and you can use the stored information related to the employees.


Drop table

A SQL drop table is used to delete a table definition and all the data from a table. When this command is executed, all the information available in the table is lost forever, so you have to very careful while using this command.

Syntax

Firstly, you need to verify the EMPLOYEE table using the following command:

Field Type Null Key Default Extra
EMP_ID int(11) NO PRI NULL
EMP_NAME varchar(25) NO NULL
PHONE_NO NO int(11) NULL
ADDRESS YES NULL char(30)
  • 4 rows in set (0.35 sec)

This table shows that EMPLOYEE table is available in the database, so we can drop it as follows:

Now, we can check whether the table exists or not using the following command:

As this shows that the table is dropped, so it doesn't display it.


SQL DELETE table

In SQL, DELETE statement is used to delete rows from a table. We can use WHERE condition to delete a specific row from a table. If you want to delete all the records from the table, then you don't need to use the WHERE clause.

Syntax

Example

Suppose, the EMPLOYEE table having the following records:

EMP_ID EMP_NAME CITY PHONE_NO SALARY
1 Kristen Chicago 9737287378 150000
2 Russell Austin 9262738271 200000
3 Denzel Boston 7353662627 100000
4 Angelina Denver 9232673822 600000
5 Robert Washington 9367238263 350000
6 Christian Los angels 7253847382 260000

The following query will DELETE an employee whose ID is 2.

Now, the EMPLOYEE table would have the following records.

EMP_ID EMP_NAME CITY PHONE_NO SALARY
1 Kristen Chicago 9737287378 150000
2 Russell Austin 9262738271 200000
4 Angelina Denver 9232673822 600000
5 Robert Washington 9367238263 350000
6 Christian Los angels 7253847382 260000

If you don't specify the WHERE condition, it will remove all the rows from the table.

Now, the EMPLOYEE table would not have any records.


Next TopicDBMS SQL Select




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