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Data selection in the SQL consists of using the
SELECT keyword. The primary formula to follow is:
SELECT What FROM WhatObject;
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The What factor can be the name of a column of
a table or query. The WhatObject factor can be the name of a table
or a query.
To specify the column you want to select, replace the
What factor in the syntax with the name of the desired column. Here
is an example:
SELECT LastName FROM Employees;
To select everything from a table or query, you can
use the asterisk as the What factor of our formula. For example, to
select all records, you would use the statement as follows:
SELECT * FROM Employees;
Alternatively, you can precede the * with the ALL
keyword. Here is an example:
SELECT ALL * FROM Employees;
To consider more than one column in a statement, you
can list them in the What factor of our formula, separating them
with a comma. The formula to use is:
SELECT Column1, Column2, Column_n FROM WhatObject;
Here is an example:
SELECT FirstName, LastName, HourlySalary
FROM Employees;
When writing the name of a table, a query, or a
column, if it's in more than one word, you must include it in square
brackets. To be safe, even if the name is in one word, you should still
include it in square brackets. Based on this, the above statement would be
written as follows:
SELECT * FROM [Employees];
Another suggestion you can use is to qualify the name
of each column to indicate the table or query it belongs to. To do this,
type the name of the table or query, followed by a period, followed by the
name of the column or the *. Here is an example:
SELECT Employees.FirstName, Employees.LastName
FROM Employees;
You can also delimit each name with square brackets as
follows:
SELECT [Employees].[FirstName], [Employees].[LastName]
FROM [Employees];
The Visual Basic language is equipped with an
impressive library of functions. These functions can also be used in
queries and even included in SQL statements. The SQL interpreter of
Microsoft Access can recognize these functions as long as you use them
appropriately.
Imagine that you want to create a column in a query
and that column should hold the full name of each employee. In a column of
a table, you could use an expression such as:
Employee: [FirstName] & " " & [MiddleName] & " " & [LastName]
The SQL statement would be:
SELECT Employees.DateHired,
[FirstName] & " " & [MiddleName] & " " & [LastName] AS Employee
FROM Employees;
Imagine that you only want to include a middle initial
instead of the whole middle name. You can use the Left$ function to
retrieve the first character of the middle name and include the call to
that function in your query. Here is an example:
SELECT Employees.DateHired,
[FirstName] & " " & Left([MiddleName],1) & " " & [LastName]
FROM Employees;
In this case, some records don't
have a middle initial because they don't have a name. For the records that
don't display a middle name, we can write a conditional statement, using
the IIf() function, to check it and taking the appropriate action
accordingly. Here is the result:
SELECT Employees.DateHired,
IIf(IsNull([MiddleName]),
[FirstName] & " " & [LastName],[FirstName] & " " &
UCase(Left([MiddleName],1)) & " " & [LastName])
FROM Employees;
In the same way, you can use any of the built-in
functions we reviewed in previous lessons.