Introduction
You are now familiar with the basics of databases and how they store and manage data but it is also very important to understand how to interact with databases in other to work with data. As a data engineer, you can interact with databases using the STRUCTURED QUERY LANGUAGE or as it is commonly known “SQL”, also pronounced “the sequel”. The question therefore is:
What is a Structured Query Language?
Structured Query Language(SQL) is a standardised programming language designed for managing and manipulating relational databases. It can be used with all databases but is particularly useful when working with relational databases. It requires a language that can interact with structured data. Examples of relational databases that sequel can interact with include:
- MySQL.
- PostgreSQL.
- Oracle and
- Microsoft SQL Server.
SQL is also used to perform various operations on the data stored in a database such the CRUD Operations which are create, read, update and delate data and other operations such as querying and inserting data.
How does a database interpret or read instructions given using SQL?
A database interprets or makes meaning or sense of SQL instruction with the use of the DBMS(Data Base Management System). As a web developer, you will execute all instructions on a database using DBMS. The DBMS takes responsibility for transforming sequel instructions into a form that’s understood by the underlying database.
SQL Data Types
Numeric Data Types (Integer Types):
- INT: A standard int size. Size varies by DBMS, its usually 4 bytes.
- SMALLINT: A small integer, size varies, usually 2 bytes.
- TINYINT: A very small int, size varies, usually 1 byte.
- BIGINT: A large integer.
String Data Types
Common SQL Commands
SELECT: Retrieves data from database.
INSERT: Adds new rows to a table.
UPDATE: Modifies existing data in a table.
DELETE: Removes rows from table.
CREATE TABLE: Creates a new table.
ALTER TABLE: Modifies an existing table.
DROP TABLE: Deletes an existing table.
GRANT: Provides privileges to users.
REVOKE: Removes privileges from users.
PRIMARY KEY: Uniquely identifies each record in a table.
FOREIGN KEY: Ensures referential integrity by linking tables.
and many more commands.
SQL Uses and Advantages
SQL is a powerful tool used for interacting with and managing data in relational databases. Listed below are some key uses and applications of SQL:
Data Querying: The SQL SELECT statements can be used to retrieve data from one or more tables.
Data Manipulation: The SQL INSERT keyword can be used to insert new rows of data to table. You can also use the UPDATE keyword to update existing data within the table and delete any rows from the table using the SQL DELETE keyword.
Data Definition: SQL CREATE, ALTER and DROP keywords can be used to CREATE new databases including tables, rows, columns, ALTER existing database objects and DROP existing database objects respectively.
Data Control: You can make use of the SQL commands GRANT and REVOKE to GRANT access privileges to databases and also REVOKE users access privileges with SQL.
Transaction Control: You can also use SQL commands COMMIT, ROLLBACK and SAVEPOINT to COMMIT or save all changes made during a current transaction, ROLLBACK or undo all changes made during the current transaction and SAVEPOINT or set a point within a transaction to which you can later roll back respectively.
Other uses or advantages of the sequel include data integrity, data analysis, data reporting and data migration.
Conclusion
SQL is a powerful and flexible language used for interacting with relational databases. It provides a wide range of capabilities for querying, manipulating and managing data as well as defining and controlling database structures. In conclusion, understanding SQL is essential for working with relational databases in various applications and industries.
