LU05a - Syntax of a DQL-Select statement

As we know, SQL stands for Structured Query Language. Consequently, It should come as no surprise that SQL is indeed consistently structured. The figure below shows the structure of a exhaustive SQL statement.

• The content of this chapter is based on the 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 (;).

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.

Let's take a table Customers as shown in the figure below.

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.

Volkan Demir