It has different meanings:
One is 'Structured Query Language', which is the subject of this 'crash' course.
Another common one is as a shorthand for Microsoft SQL Server, which is a set of database software products produced by Microsoft.
Microsoft SQL Server has its own version of Structured Query Language which it calls 'Transact SQL' or 'T-SQL' for short
Other software products have their own variations of Structured Query Language. For example Oracle provides 'PL/SQL'
Although there are slight differences between the different versions of SQL, the core is exactly the same. So if you learn SQL on one product you can adapt quickly to others.
Structured Query Language is a way of interacting with relational databases
Relational databases are those which can have many tables. In theory this will be designed in such as way as to avoid duplication of data. And each table will have a unique key which allows it to be related to other tables
In real life the design and content of databases can get a bit more messy, for various reasons.
SQL is essentially an instruction, written out as text, which is 'thrown' at a database. The database will attempt to respond to the instruction
How the instructions are written and thrown - and where the results are displayed - will depend on what tools you have available, Typically there will be a utility (such as SQL Server Management Studio) which allows these things to be done in different panels visible together on the same computer screen
So we would write (or retrieve an existing) SQL script in one panel, hit an Execute button, and see the results displayed in another panel
.
The beauty of SQL is that the core is relatively simple
There are different types of instruction for different purposes
Computer people give these grand titles such as
- Data Manipulation Language (DML)
- Data Definition Language (DDL)
- Data Control Language (DCL)
These are basically just groups of instructions for either doing things with data or setting things up
SQL Data Manipulation Language (DML) is mainly based around the following four types of instruction
- SELECT
- DELETE
- INSERT
- UPDATE
These instructions are used for looking at, getting rid of, collecting or changing data
Of these, SELECT is the most often used as it is the one that actually gives the answers to any questions
SQL Data Definition Language (DDL) is mainly based around the following three types of instruction
- CREATE
- ALTER
- DROP
These instructions are the ones needed to set things up - and then changing them again later. We will not spend much time looking at these on this crash course
SQL Data Control Language (DCL)is mainly based around the following three types of instruction
- GRANT
- REVOKE
- DENY
These are the instruction used to set out who can do what. Computer people are obsessed with stopping other people doing things, or looking into the innards of their creations. It's a shame as otherwise they are good people to have around. We will not spend any time looking at these 'permission' issues on this crash course. Just be ready to hit this nonsense when you try to use anything in the workplace
That is the end of Part 1.
In Part 2 we will look at SELECT - the main big thing you will need to master
Here are a few links which may help flesh out the content of Part 1
https://www.w3schools.com/sql/sql_intro.asp
https://www.infoworld.com/article/3219795/sql/what-is-sql-structured-query-language-explained.html
https://bytescout.com/blog/what-is-sql-and-what-is-it-used-for.html
https://www.ntchosting.com/encyclopedia/databases/structured-query-language/
https://searchsqlserver.techtarget.com/definition/SQL
No comments:
Post a Comment