Category: Database

To delete a column in SQL we will be using DROP COLUMN method: ALTER TABLE employees DROP COLUMN age; We will start off by giving the keywords ALTER TABLE, then we will give the name of the table, following which we will give the keywords DROP COLUMN and finally give the name of the column which we would want to remove.... Read Mores

Our database comprises of a lot of different entities such as tables, stored procedures, functions, database owners and so on. To make sense of how all these different entities interact, we would need the help of schema. So, you can consider schema to be the logical relationship between all the different entities which are present in the database. Once we have a clear understanding of the schema, this helps in a lot of ways: We can decide which user has access to which tables in the data... Read Mores

We have four types of SQL Queries: DDL (Data Definition Language): the creation of objects DML (Data Manipulation Language): manipulation of data DCL (Data Control Language): assignment and removal of permissions TCL (Transaction Control Language): saving and restoring changes to a database Let’s look at the different commands under DDL: Command Description CREATE Create objects in the database ALTER Alters the structure of the database object DR... Read Mores

Different database management systems have different queries to see all the tables. To see all the tables in MYSQL, we would have to use this query: show tables; This is how we can see all tables in ORACLE: SELECT table_name FROM User_tables; This is how we can extract all tables in SQL Server: SELECT * FROM Information_schema.tables; ... Read Mores

Joins are used to combine rows from two or more tables, based on a related column between them. Types of Joins: • INNER JOIN − Returns rows when there is a match in both tables. • LEFT JOIN − Returns all rows from the left table, even if there are no matches in the right table. • RIGHT JOIN − Returns all rows from the right table, even if there are no matches in the left table. • FULL OUTER JOIN − Returns rows when there is a match in one of the tables. • ... Read Mores

We will be using the DELETE query to delete existing rows from the table: DELETE FROM table_name WHERE [condition]; We will start off by giving the keywords DELETE FROM, then we will give the name of the table, after that we will give the WHERE clause and give the condition on the basis of which we would want to delete a row. For example, from the employee table, if we would like to delete all the rows, where the age of the employee is equal to 25, then this will the command: DELETE... Read Mores

This is the command to change a table name in SQL: ALTER TABLE table_name RENAME TO new_table_name; We will start off by giving the keywords ALTER TABLE, then we will follow it up by giving the original name of the table, after that, we will give in the keywords RENAME TO and finally, we will give the new table name. For example, if we want to change the “employee” table to “employee_information”, this will be the command: ALTER TABLE employee RENAME TO employee_information... Read Mores

There are two ways to delete a table from sql: DROP and TRUNCATE. The DROP TABLE command is used to completely delete the table from the database. This is the command: DROP TABLE table_name; The above command will completely delete all the data present in the table along with the table itself. But if we want to delete only the data present in the table but not the table itself, then we will use the truncate command: DROP TABLE table_name ; ... Read Mores