The SELECT statement is used to select data from a database.
The result is stored in a result table, called the result-set.
SQL SELECT Syntax is
This statement select only one column of the database field.
|
| SELECT column_name(s) FROM table_name | |
|
This SQL statement select all the fields of the database using the (*) asterisk
SELECT * FROM table_name
Heres the sample SQL statement below.
Figure 1
Select IDNo,LastName,FirstName,MI FROM EmployeeTbl Where IDNo= 12345
Figure 2
Select * FROM EmployeeTbl Where IDNo=12345
A SQL
SELECT statement can be broken down into numerous elements, each beginning with a keyword. Although it is not necessary, common convention is to write these keywords in all capital letters. In this article, we will focus on the most fundamental and common elements of a
SELECT statement, namely
The SELECT ... FROM Clause
The most basic SELECT statement has only 2 parts: (1) what columns you want to return and (2) what table(s) those columns come from.
If we want to retrieve all of the information about all of the customers in the Employees table, we could use the asterisk (*) as a shortcut for all of the columns, and our query looks like
SELECT * FROM Employees
If we want only specific columns (as is usually the case), we can/should explicitly specify them in a comma-separated list, as in
SELECT EmployeeID, FirstName, LastName, HireDate, City FROM EmployeesTable
The WHERE Clause
The next thing we want to do is to start limiting, or filtering, the data we fetch from the database. By adding a
WHERE clause to the
SELECT statement, we add one (or more) conditions that must be met by the selected data. This will limit the number of rows that answer the query and are fetched. In many cases, this is where most of the "action" of a query takes place.
We can continue with our previous query, and limit it to only those employees living in London:
SELECT EmployeeID, FirstName, LastName, HireDate, City FROM Employees WHERE City = London
The ORDER BY Clause
Until now, we have been discussing filtering the data: that is, defining the conditions that determine which rows will be included in the final set of rows to be fetched and returned from the database. Once we have determined which columns and rows will be included in the results of our
SELECT query, we may want to control the order in which the rows appear—sorting the data.
To sort the data rows, we include the
ORDER BY clause. The
ORDER BY clause includes one or more column names that specify the sort order. If we return to one of our first
SELECT statements, we can sort its results by City with the following statement:
SELECT EmployeeID, FirstName, LastName, HireDate, City FROM EmployeesTable
ORDER BY City
