A "select dynamic" field (or dynamic drop-down list) creates a menu (or drop list) with a single choice.

Definition

A "select dynamic" field (or dynamic drop-down list) creates a menu (or drop list) with a single choice. It must contain at least one option. The field options are generated by the query filled in the configuration field. An option consists of a "text" part and a "value" part. The "text" is the text displayed in the form input and the "value" is the value recorded (likely to be used in a search form) after form submission.
select-dynamic-overview

Settings

select_dynamic_settings

Common Plugin Settings (Link to the article)

Query (Required)

Select a builder mode

Construction

Assisted creation of the query to automatically fill field options ("text" and "value").

Default Value

Optional, the default write by copying only the value of an option already assigned to this field. It is applied to first load the form, primarily on the "label selection" (previous parameter). * (Override) The default value of a field is overwritten by the value entered directly into the editing interface for a content type, see Step

Select Label

Write the first option in the dropdown list, any value associated with this option is recorded (zero). It is generally used to prompt the user to "select an option" or to indicate the type of options, such as "select a living"

Data table

Select the data table where are stored field options.

Options Name

Select the field used for the text of options.

Where

Write an SQL condition (clause), refer to SQL terms.

Options Value

Select the field used for the value of options.

Order By

Write a "Order By" condition, like the name of a field.

Multiple

Enable or not the multiple mode by selecting "Yes" or "Not". It transforms the drop down list to allow multiple selections.

Language Detection

Select Joomla language or GeoIP language. If your data table manage a language field, you can enable the detection of the language and drop down list will be filter by this language. To use GeoIP, you must enable GeoIP module from Apache.

Language Codes / Default

Write language codes

Add Static Options

Free (developer)

Manual creation of the SQL query to automatically fill field options ("text" and "value"). Syntax of the SQL query must be like:
Field_name_1 AS SELECT text, field_name_2 AS value FROM #__table
						
(replace Field_name_1 and field_name_2 by your own fields, and #__table by your datatable name). Add any SQL words like WHERE, LIMIT ... Example: list all links from a Joomla menu
SELECT title AS text, link AS value FROM [#__menu] WHERE menutype = 'mainmenu'
						
The field will be formed by the list of "Mainmenu" menu links.

Uses

This field is a good alternative to "select single" field if the list of options is large and dynamic like for countries, cities, postal codes, categories, users.
Often use to select only categories from a specific parent category when you want to save a content only in this children categories.

List of parameters accessible from a template

value, text, options []?, default_value, ... to be completed (if generic, not to put here).