Using Arguments in SELECT Statements

IN THIS PAGE

What is an Argument?
A Demonstration Script
Using an Argument
Creating an Argument
Structuring the Script

Description

How to create and use Arguments, and structure scripts, relating to Select statements.

What is an Argument?

An argument is a value that is interpreted at run-time and inserted into a SQL statement. You use the SQL::Arguments? object to pass one or more arguments to AlphaDAO. A SQL statement may use any number of arguments. An argument may be of any of the following data types.

"B" = blob
"C" = character
"D" = date
"L" = logical
"N" = numeric
"T" = time
"Y" = short time

A Demonstration Script

Open the Code Editor and create a new script with the following content. This script prompts for a city value, then displays the records that contain that value in the bill_city field of the AlphaSports customer table.

dim conn as SQL::Connection
dim sql as C
dim vCity as C
dim args as SQL::Arguments
vCity = ui_get_text("City", "Show Companies in what city?")
sql = "select lastname, firstname from customer where bill_city = :city Order By Company"
if .not. conn.open("{A5API=Access,FileName='C:\Program Files\a5v8\MDBFiles\Alphasports.mdb', UserName='Admin'}")
    ui_msg_box("Error", conn.CallResult.text)
    end
end if
if .not. args.Set("city", vCity)
    end
end if
if .not. conn.execute(sql, args)
    ui_msg_box("Error", conn.CallResult.text)
    end
end if
sql_resultset_preview(conn.resultset)

Using an Argument

You use an argument by preceding its name with a colon (:), as in :city.

... where bill_city = :city ...

Creating an Argument

You create an argument in a two step process. First, you create the SQL::Arguments object. Then you add elements to it with the .Set(?) or .Add(?) methods.

dim args as SQL::Arguments
if .not. args.Set("city", vCity)
    end
end if

Structuring the Script

Note the way the script tests the return value of many of the methods, and ends when a failure occurs. Because most of these AlphaDAO methods return .T. (TRUE) for success, this is a good way of terminating a script that is not working.

if .not. conn.execute(sql, args)
    end
end if

A more complete application would add some error handling. At a minimum, you might display an error message before exiting.

if .not. conn.execute(sql, args)
    ui_msg_box("Error", conn.CallResult.text)
    end
end if

If you run this script and enter "Boston", you will see: Picture