Select in two MySQL tables

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:
Let's see some examples, in which we'll use the following two tables, named "categories" and "links".

categories

id	category
1	PHP-MySQL
2	HTML

links

id	link	visits
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. 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'. 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'). 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. 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.

<a href="http://coursesweb.net/" title="CoursesWeb.net">CoursesWeb.net</a>

h2 {
  font-family:"Calibri",sans-serif;
}

var elm_list = document.querySelectorAll("div.cls");
var nr_elms = elm_list.length;       // number of selected items
alert(nr_elms);

$arr =[1, 2, 3, 4);
$arr_sum = array_sum($arr);
echo $arr_sum;       // 10