LU06a - Syntax of a DQL-Select statement [BZZ

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====== LU06a - Syntax of a DQL-Select statement ======

As we know, **SQL** stands for **S**tructured **Q**uery **L**anguage. Consequently, It should come as no surprise that SQL is indeed consistently structured. The figure below shows the  structure of a exhaustive SQL statement.

{{:modul:m290:learningunits:lu04:theorie:sql-syntax.png?600|}}

===== NOTES  =====
  * The content of this chapter is based on the  [[https://www.w3schools.com/sql/sql_syntax.asp|W3School-SQL-tutorial]].
  * Please note that the use og CAPITAL LETTERS for SQL commands and tabs can make it easier for you to maintain your program code. 
  * Make sure, that every complete sql statement is finished by a semicolon (;).

===== The Syntax of DML commands =====
Every SQL query is composed by three main commands:

  * **SELECT** myColumn1, myColumn2, ... [or * for all columns]
  * **FROM** myTable
  * **WHERE** myCondition. 
  * **ORDER BY** myColumn2 **ASC|DESC**;

With **SELECT** we specify which columns we want to retrieve, with **FROM** we specify the TABLE from which the columns originate, with **WHERE** we determine the condition under which the data records are selected, and finally, with **ORDER BY** +  **[ASC | DESC]** we define the order in which the result set is to be displayed on the screen. 

===== Basic example =====
Let's take a table **Customers** as shown in the figure below. 

{{:modul:m290:learningunits:lu04:theorie:screenshot_2024-08-30_095010.png?700|}}

To retrieve all the information, which are stored in this table, our SQL command would be like follows. 

   SELECT * 
   FROM Customers;

or as a more detailed notation

   SELECT CustomerID, CustomerName, ContactName, Address, City, PostalCode, Country
   FROM Customers;
   
The result set would include the entire contents of the table, since we we have not defined any preconditions or filters. 









===== Vocabulary =====
^ English ^ German ^
| precondition | Vorbedingung |
| exhaustive  | erschöpfend, vollständig |
| clause | Abschnitt | 
| to determine | bestimmen |
| to fetch | abrufen, holen | 
| be composed by | besteht aus | 
| notation | Schreibweise |

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[[https://creativecommons.org/licenses/by-nc-sa/4.0/|{{https://i.creativecommons.org/l/by-nc-sa/4.0/88x31.png}}]] Volkan Demir