Tag: important sql queries

The technology world is using data for almost everything. However, only data has no value alone. Here is SQL, that’s Structured Query Language. SQL makes it possible for a person to work with all the data involved in organizations by efficiently managing and manipulating vast datasets. In this beginner's guide to SQL by a online web development course instructor in Delhi, we will explore the various important aspects of SQL as a language from queries to why mastering it is important for any aspiring database developer. What is SQL? SQL stands for Structured Query Language; it can be defined as specialized programming language used to communicate with databases and manipulate their contents. The word "Structured" signifies that SQL employs an orderly methodology on how people interrelate with databases and request information. SQL uses CRUD operations; create, read, update and delete on a database. It is basic for managing databases and other related tasks such as data manipulation among others. Unlike other general purpose programming languages like Java or C++, SQL is specifically designed for DMBSs (Data Base Management Systems) making it a fourth generation language (4GL). Sometimes called sequel or ess-que-el. It has particular role like no other. Each time you come across words such as loops, logic directives, variables they are useful for developers who use this programming language for writing statements that can be applied when building websites or any software using front-end or back-end languages. SQL is still serving as a query language focused on storing/retrieving/manipulating data in databases itself. SQL Language Elements SQL works at the level of a structure through the series of statements that begin with keywords or commands such as CREATE and end with a semicolon. These statements are responsible for the core SQL operations. Here are some key SQL language elements: Keywords: used to perform different functions within a database. Examples include ADD, JOIN, and VIEW. Identifiers: these would be object names existing in the database like tables, views, indexes, columns. Expressions: strings of symbols/symbols which do mathematical operations on data. Search Conditions: criterion for selecting just part of rows in a table or creating IF statement checking condition in row itself. Data Types: when creating a table you need these to specify what type of data is stored in each column. The most common ones are number, string and date. Nulls: represent unknown values or missing information in databases. Comments: utilized to explain sections of sql statements for better understandability and maintainability. Important SQL Queries for Beginners These are some of the most important SQL queries for beginners. First let us create one table and then use it for our queries guide CREATE TABLE ads ( ads-id INT PRIMARY KEY, ad-cname VARCHAR(50), cost INT ); Lets insert one row of data INSERT INTO ads (ads-id, ad-cname, cost) VALUES (1, 'video', 30 L), (2, 'audio', 20 L), (3, 'photo', 5 L); Retrieving Data From All Columns Retrieving data from all columns of a table is a fundamental SQL operation. The query that does this is simple. Instruct SQL to fetch any column by using the asterisk (*) after the SELECT statement without listing them out individually. After the FROM clause, do not forget to specify the name of the table. For example, if we want to retrieve data from “ads” table, we will use the following query: SELECT * FROM ads; ADS-IDAD-CNAMECOST1Video30 L2Audio20 L3Photo10 L Retrieving Data From Certain Columns This is one of the simplest SQL operations which involves getting data from certain tables’ columns. It’s rather easy to execute this type of query, though. A plain SQL query will be able to select certain columns. List them down separately by inserting an asterisk (*) after SELECT keyword – a special character that tells an oracle server to bring back everything in this particular row. Just remember also (afterwards) include your table name on FROM clause like this one; SELECT ad-id, ad-cname FROM ads; It will give only ads-ID coloum and ad-cname coloum data Filtering Data Using the WHERE Clause SQL filtering is important as it helps you extract specific records based on given conditions only through WHERE clause which narrows down your search results making it faster and better targeted than before. By using where clause you can filter data according to certain standards. For instance, given a query below would return only those records where age is 2 or more: SELECT ad-id, ad-cname, cost FROM animal WHERE cost >= 2; Filtering Data Using Conditions Joined by AND Operator The AND operator is crucial when filtering data using multiple conditions since it allows combining conditions where each condition has its own criteria; thus fulfilling all of them at once. Now consider a situation where you are interested in retrieving rows that have value greater than or equal 2 for age column and whose names contain dog in it;