{"id":31,"date":"2022-02-07T16:29:18","date_gmt":"2022-02-07T16:29:18","guid":{"rendered":"https:\/\/openquery.com\/?p=31"},"modified":"2022-02-28T13:55:55","modified_gmt":"2022-02-28T13:55:55","slug":"what-is-a-query-in-sql","status":"publish","type":"post","link":"https:\/\/openquery.com\/what-is-a-query-in-sql\/","title":{"rendered":"What Is A Query In SQL?"},"content":{"rendered":"\n
The Q in SQL stands for Query, so, as you can glean, it\u2019s a pretty crucial aspect of this database language, but what does it mean exactly, and how is a query built in SQL? <\/p>\n\n\n\n
Well, that\u2019s exactly what I\u2019m going to guide you through here today.<\/p>\n\n\n\n
While the nuances of data languages may appear daunting at first, they\u2019re all actually very simple, designed to help rather than hinder us. Stick with me, and you\u2019ll see exactly what I mean!<\/p>\n\n\n\n
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What Is SQL?<\/strong><\/h2>\n\n\n\n
The key to understanding queries, or anything about data languages really, is to start with the big picture and work your way down to specifics, so let\u2019s begin with an SQL definition.<\/p>\n\n\n\n
Now, you already know what the \u201cQ\u201d stands for, but what about the \u201cS\u201d and the \u201cL\u201d? Any ideas? All together, SQL is an abbreviation of Structured Query Language.<\/p>\n\n\n\n
In a nutshell, SQL is a standardized computer language that helps us to navigate and manage computer databases\u2026 that\u2019s it. <\/p>\n\n\n\n
It\u2019s just a very simple code set we can use to make our lives easier when we\u2019re dealing with large databases.<\/p>\n\n\n\n
Got It, But Where Do Queries Come In?<\/strong><\/h2>\n\n\n\n
Databases are all about storing data and answering our questions. <\/p>\n\n\n\n
If we need to know something, we can consult the database and find the relevant information, but here\u2019s the thing\u2026 databases and database objects can be HUGE!<\/strong><\/p>\n\n\n\n
Searching for very specific bits of data in complex databases manually is like searching for a needle in a freakin\u2019 needle stack, so we need a tool that refines our search and guides us directly to the data we\u2019re hoping to find\u2026 this is where querying comes in.<\/p>\n\n\n\n
Truth be told, there\u2019s really no difference in core meaning between an SQL query and the actual English language word, \u201cquery\u201d \u2014 they both mean \u201cquestion\u201d, or in more \u201ccomputery\u201d terms, requests for data.<\/p>\n\n\n\n
What kind of question, you ask? Well\u2026 any question really. If the database has the data, you can ask a question about it.<\/p>\n\n\n\n
Let\u2019s say, for example, we have a database of album details, and one object within our album database is dedicated to Beatles albums, and perhaps this table is called tblBeatles and contains the following data: Album ID \u2014 Album Title \u2014 Release Date \u2014 Rating. <\/p>\n\n\n\n
We may be interested to know the number of Beatles albums that were released during and prior to 1964.<\/p>\n\n\n\n
Now, if we were asking a Beatles superfan, we might phrase the question along the lines of\u2026 \u201cDo you know how many Beatles albums were released during or before 1964?\u201d<\/p>\n\n\n\n
But remember, we\u2019re dealing with a computer here, and SQL is built from the ground up to navigate databases, so we have to phrase our query differently. Here\u2019s how it\u2019s done!<\/p>\n\n\n\n
How To Build A Query In SQL<\/strong><\/h2>\n\n\n\n
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Building a query in SQL is all about taking your \u201chuman\u201d question, and replacing the constituent parts of the sentence with keywords in the SQL dictionary. <\/p>\n\n\n\n
These keywords will tell the computer what to look for (as in field), where to look for it (as in table), and how to look (the conditions of your request).<\/p>\n\n\n\n
Rather confusingly, the corresponding keywords to \u201cWhat\u201d, \u201cWhere\u201d, and \u201cHow\u201d are:<\/p>\n\n\n\n
Select <\/strong>(What)<\/p>\n\n\n\n
When we type in Select<\/strong>, we are essentially telling our computer to go and retrieve something from a certain database or table.<\/p>\n\n\n\n
From<\/strong> (Where)<\/p>\n\n\n\n
When we follow it up with From<\/strong>, we\u2019re telling our computer where to retrieve the data from.<\/p>\n\n\n\n
Where<\/strong> (How)<\/p>\n\n\n\n
When we finish things off with Where<\/strong>, we\u2019re disclosing the criteria of our request.<\/p>\n\n\n\n
So, our human query, \u201cHow many Beatles albums were released during or prior to 1964?\u201d ends up looking a little something like this\u2026<\/p>\n\n\n\n
Select <\/strong>Album Title<\/p>\n\n\n\n
From<\/strong> tblBeatles<\/p>\n\n\n\n
Where <\/strong>Release Date <= 1964<\/p>\n\n\n\n
Our computer will then generate the following list:<\/p>\n\n\n\n
As you can see, our computer has given us the bare minimum information, which is a list of the Beatles albums released during or before 1964, and that is what we asked for, but I bet you expected to see at least the release dates listed as well, right?<\/p>\n\n\n\n
Well, while our human Beatles superfan may understand that the implication of the question was to elaborate in certain areas, our computer does not. <\/p>\n\n\n\n
We need to be very specific with SQL, as computers can only operate in very literal ways.<\/p>\n\n\n\n
Creating Detailed Queries<\/strong><\/h2>\n\n\n\n
To add more details, we need to modify our query. For instance, if we wanted the release dates listed as well as the titles, our query becomes\u2026<\/p>\n\n\n\n
Select<\/strong> Album Title, Release Date<\/p>\n\n\n\n
From<\/strong> tblBeatles<\/p>\n\n\n\n
Where<\/strong> Release Date <= 1964<\/p>\n\n\n\n
Simple, right? But what if we wanted the results to arrive with all fields of information in the table? Would that mean we have to type in each individual field after \u201cSelect\u201d?<\/p>\n\n\n\n
Thankfully, no.<\/p>\n\n\n\n
All we have to do to specify that we want all fields in our results is to add an asterisk after \u201cSelect\u201d, leaving our query looking a little something like this\u2026<\/p>\n\n\n\n
Select <\/strong>*<\/p>\n\n\n\n
From<\/strong> tblBeatles<\/p>\n\n\n\n
Where<\/strong> Release Date <= 1964<\/p>\n\n\n\n
Adding More Conditions<\/strong><\/h2>\n\n\n\n
If we then wanted to add more conditions to the \u201cWhere\u201d stage of our query, all we have to do is separate them with a big, fat AND, which would look like\u2026<\/p>\n\n\n\n
Select<\/strong> *<\/p>\n\n\n\n
From<\/strong> tblBeatles<\/p>\n\n\n\n
Where<\/strong> Release Date <= 1964<\/p>\n\n\n\n
AND<\/strong><\/p>\n\n\n\n
Rating >= 8<\/p>\n\n\n\n
Now our list would include all Beatles albums released in or before 1964 that are rated at 8 or above, as well as all fields of information corresponding to the shortlisted albums, but that\u2019s not all we can do!<\/p>\n\n\n\n
Adding More Modifiers<\/strong><\/h2>\n\n\n\n
We can use additional keywords to modify how the results of a query are presented to us. <\/p>\n\n\n\n
Say, for instance, that we want our results to be listed by rating, we can add the keyword \u201cOrder By\u201d to our command chain, followed by \u201cRating\u201d,<\/p>\n\n\n\n
\u201cGroup By\u201d is another cool modifier that will group sourced data in accordance with a certain criterion. <\/p>\n\n\n\n
What\u2019s more, if you\u2019re dealing with a particularly large database object, and you don\u2019t want it to pull up every single possible result, you can add a \u201cLimit\u201d modifier to the end, followed by the number of results you want, i.e. Limit <\/strong>100.<\/p>\n\n\n\n
Final Thoughts<\/strong><\/h2>\n\n\n\n
There you have it, folks \u2014 the basics of querying in SQL. <\/p>\n\n\n\n
Now, bear in mind that we\u2019ve only just scraped the surface here today. SQL queries can be as simple or complex as you like, so be sure to familiarize yourself with code syntax and experiment with lots of different requests. <\/p>\n\n\n\n
You\u2019ll be a database wiz in no time!<\/p>\n\n\n\n
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