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For 2021 - online Python 3 training - see ((here)).

Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
We can now offer tailored online training - small groups, real tutors - works really well for groups of 4 to 14 delegates. Anywhere in the world; course language English.

Please ask about private 'maintenance' training for Python 2, Tcl, Perl, PHP, Lua, etc.
How do I query a database (MySQL)?

From my mailbox ... "What are the different ways of queries in databases? Could u pls explain each way in more detail? thanks"

The term "query" means something a little bit different in the term "SQL" to it does in regular English usage - the dictionary definition is to ask for information / pose a question, but as a part of SQL ("structured query language"), it means and request of a database and that can include:
• Setting up and modifying table structures
• Inserting and modifying data held in tables
• retrieving information about the structure of tables and how the database is running
• retrieving information from the tables of a database - the actual data.
Only the last of those is a "query" in terms of normal English usage.

All SQL database queries [exception - Microsoft Access] are made via a service or daemon - a process running on a server computer. That process is designed to provide the one and only route to the data, so that multiple concurrent users will be able to work together on the same information with no risk of one adversely effecting the other through lack of syncronisation. And the requests passed to that service (Microsoft word) or daemon (unix / Linux word) will be in "SQL".

SQL queries all start with a keyword such as CREATE (to create a table), INSERT (to insert data) or SELECT (to retrieve the actual information held). And they are the ONLY way to access the database. However, they are not very easy (they are not designed to be easy!) for the human user - they are much more easily formed within another program, with the human user calling that other program as his / her interface to the data. For example, if you were to book a hotel room or training course with us, a number of database 'queries' would be run - SELECTs mostly with a few INSERTs - in the process, which would be completely hidden from you. Indeed, you've probably done some SELECTs without realising it to read our web site already, as almost every page has some database access.

I can explain SQL, and SELECTs, in much more detail - but there are whole books on the subject - it's massive. So that explanation would usually be a part of one of our courses, in which we would cover some elements of database design, as well as how to access the data. Such a course would be useful if you'll be accessing the data directly in your own programs (in languages such as Perl, PHP, or Python), but it's really not necessary for you to learn SQL just to use a web site that makes use of it internally. If everyone who stayed at our hotel was required to know SQL before they booked, it would be a strange world.

Some further links for you:
(next course is on 13th and 14th August and we currently have places available)
(that's an example of a SELECT showing each of the elements in the command)
(A link to our MySQL FAQ - many common questions answered)
(written 2009-06-15, updated 2009-06-22)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
S152 - SQL Primer as Used in MySQL
  [158] MySQL - LEFT JOIN and RIGHT JOIN, INNER JOIN and OUTER JOIN - (2004-12-20)
  [270] NULL in MySQL - (2005-04-06)
  [494] MySQL - a score of things to remember - (2005-11-12)
  [502] SELECT in MySQL - choosing the rows you want - (2005-11-22)
  [515] MySQL - an FAQ - (2005-12-03)
  [591] Key facts - SQL and MySQL - (2006-02-04)
  [3060] INSERT, DELETE, REPLACE and UPDATE - changing the content of SQL tables - (2010-11-19)
  [3061] Databases - why data is split into separate tables, and how to join them - (2010-11-20)
  [4007] Which database should I use? MySQL v SQLite - (2013-02-16)

S050 - MySQL - General
  [2053] What a difference a MySQL Index made - (2009-02-25)
  [2085] MySQL - licensing issues, even with using the name - (2009-03-16)
  [2134] Oracle take over Sun who had taken over MySQL - (2009-04-21)
  [2426] Which version of MySQL am I running? - (2009-09-26)
  [2559] Moving the product forward - ours, and MySQL, Perl, PHP and Python too - (2010-01-01)
  [2561] The future of MySQL - (2010-01-03)
  [2567] Extra MySQL course dates (2 day course, UK) - (2010-01-08)
  [2861] MySQL and Java - connectivity past, present, and future thoughts - (2010-07-09)
  [3361] Blowing our own trumpet - MySQL resources - (2011-07-18)

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Perl references - $$var and \$var notations
How do I query a database (MySQL)?
Cornerstone Cafe, Melksham
Handling nasty characters - Perl, PHP, Python, Tcl, Lua
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Alumni - revisiting and supporting the old University
Sending awkward characters by email in Perl
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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