Php-mysql Course

In this tutorial you can learn how to select data from two MySQL tables with a single query.
When the SQL query selects columns from diferent tables, you must specify the table name and the column; the syntax is:
SELECT `table1`.`column`, `table2`.`column` FROM `table1`, `table2` WHERE conditon

Let's see some examples, in which we'll use the following two tables, named "categories" and "links".
categories
idcategory
1 PHP-MySQL
2 HTML
links
idlinkvisits
1 coursesweb.net/php-mysql/arrays 12
1 coursesweb.net/php-mysql/strings 15
2 coursesweb.net/html/html-tables 18

1. Select all the columns from "categories" table where id=2, and the "link" and "visits" columns where visits>13.
SELECT `categories`.*, `links`.`link`, `links`.`visits` FROM `categories`, `links` WHERE `categories`.`id`=2 AND `links`.`visits`>13
Result:
| id | category |                link             | visits |
-----------------------------------------------------------------
| 2 |   HTML    | coursesweb.net/php-mysql/strings |   15   |
| 2 |   HTML    | coursesweb.net/html/html-tables  |   18   |


2. Select the "category", and the "link" columns, where the 'id' in the 'categories' table is 1 and the id in the 'links' table is equal with the 'id' of the 'categories'.
SELECT `categories`.`category`, `links`.`link` FROM `categories`, `links` WHERE `categories`.`id`=1 AND `categories`.`id`=`links`.`id`
Result:
| category  |               link                   |
----------------------------------------------------
| PHP-MySQL | coursesweb.net/php-mysql/arrays  |
| PHP-MySQL | coursesweb.net/php-mysql/strings |

Two Selects in a Query

You can also perform two select commands in a SQL query.
Examples:

1. Select the "link" column (from 'links') where the "id" corresponds to the HTML value (stored in the 'categories').
SELECT `link` FROM `links` WHERE `id`=(SELECT `id` FROM `categories` WHERE `category`='HTML')
Result:
|               link                  |
---------------------------------------
| coursesweb.net/html/html-tables |


2. Counts all rows in the 'links' table, where visits>14, and selects "category" column from 'categories' where id<4.
SELECT (SELECT COUNT(*) FROM `links` WHERE `visits`>14) AS nrl, `category` FROM `categories` WHERE `id`<4
Result:
| nrl | category  |
-------------------
|  2  | PHP-MySQL |
|  2  |   HTML    |

- There is also another way to select columns from two tables in a single query, by using the JOIN command. This method is presented in the next tutorial.

Daily Test with Code Example

HTML
CSS
JavaScript
PHP-MySQL
Which tag create a highlighted bolded text?
<q> <strong> <em>
<p>Address: <strong>http://CoursesWeb.net/</strong> - Tutorials.</p>
Which of these CSS codes displays the text bolded?
text-size: 18px; font-style: italic; font-weight: 800;
#id {
  font-weight: 800;
}
What JavaScript function can be used to call another function multiple times, to a specified time interval?
setInterval() setTimeout() push()
function someFunction() { alert("CoursesWeb.net"); }
setInterval("someFunction()", 2000);
Click on the correctly defined variable in PHP.
var vname = 8; $vname = 8; $vname == 8;
$vname = 8;
echo $vname;
Select in two MySQL tables

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