Basics of SQL

SQL is short for “Sequential Query Language” and is the predominate way for applications to request data from a relational database. In layman’s terms, its a language we use to get data from storage quickly.

The SQL language is a language that is based on creating relationships between different tables by unique identifiers (or ID’s). Essentially SQL allows you to use these relationships to link records together so that reports can be created. It’s not a hard language to learn either, and is pretty easy to read with a bit of practice.

Anatomy of a SQL Statement

Here’s a very basic break down of what makes up a SQL statement. Most SQL statements comprise of a few common elements.

  • Column Titles are the references to where the data is within the table. They appear throughout the statement and are titles. Common practice is to keep these lower case.
  • Table Names are also references to where the data within a table can be found. They can be attached to column names with a period (Ex. “table_name.column_name”). New tables are defined usually after the FROM statement.
  • Relationships – Relationships are often donated with a “JOIN” and always found after the FROM statement. Some relationships are also found in the where.
  • Conditions – Found after the “WHERE” of the statement and always comprise of an operator (ex. “=”, “>”, “<“).
  • Orders – Are a list of fields and define the order the data shows. They can be dedicated ascending (ex. “ASC”) or descending (ex. “DESC”) abilities.
  • Data – Found on one side of the equation, or within the UPDATE, INSERT, and REPLACE statements for importing.
  • Operations – Operations modify data or comprise data from existing data. These can provide mathimatical functions, such as averages. Or they’re equally adapt at handling string manimuplations, like putting two fields together.

Types of SQL Statements

There are many types of SQL statements someone can write. Due to convention, these are commonly capitalized.

SELECT

A SQL “select” is a statement for requesting or retreiving data from the database.

INSERT

Inserts are exactly what they sound like. They’re creating new records in the database and add new data.

UPDATE

Updates change current data. Or surprise, it updates it.

DELETE

Deletes delete a record from the database. Many systems do not use these as its common to use a field to hide the data instead.

And a few others

There are a few other types of statements but are beyond the scope of this brief introduction to SQL. These statements can setup and update the database struture. And can even create things like indexes which can improve (or hurt) performance.

Common Problems Associated with SQL Queries

Sounds pretty basic right? We’ll not so fast. SQL suffers from a common, and preventable, security concern called SQL injections. Ignorance and bad practices in coding are what cause it.

Poorly written SQL statements can also be very slow. Crashing your server or allowing malicious attackers a potential target for denial of service attacks.

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