Basics of SQml^TM-Web

This section covers the following:

• Brief Overview of HTML Forms
• Where SQml^TM Comes In
• Practice Examples

If you are not familiar with HTML, HTML forms, or SQL, you might want to check out some of the sites below before reading this tutorial. There are also many Beginner's Guides to HTML (just look for them with your favorite search engine):

HTML Guides:

• www-gnome.wi.mit.edu/WWW/sample_chapter/
• www.lib.stthomas.edu/ireland/htmintro/pages/forms.htm

SQL Guides:

• wonder.lancs.ac.uk/unit3/m1/
• SQL Technical Discussion

Brief Overview of HTML Forms

HTML forms must have a method and an action designated in their form tag. Form tags look something like this:

	<FORM METHOD="method" ACTION="url">.

The METHOD tells the computer how to send the information. The "post" method gives the most flexibility, so it is the one that is used most often. The URL tells the form where to send the information gathered by the input tags.

HTML input tags look something like this:

 <INPUT NAME="name" TYPE="type" VALUE="value">.

NAME is the name of the variable that will hold the value selected by the user of the form. The different input types are: text, textarea, checkbox, radio, and select (creates a pulldown menu). VALUE is the the number or text that will be associated with the NAME if the user checks a box, clicks a radio button, or selects a menu item. Text and textarea do not use the VALUE element because the value is entered by the user.

Example:

<INPUT NAME="color" TYPE="checkbox" VALUE="brown"> BROWN

 BROWN

Once we have a value associated with a name, we need a submit button. The submit button triggers the action defined in the FORM tag and the information is sent to another file for processing.

 Example: <INPUT TYPE="SUBMIT" VALUE="Submit Data">
 

For more information on HTML forms visit the sites mentioned above.

Where SQml^TM comes in

First let's start with some basic guidelines:

1. The form sending the information to the SQml^TM file must have the ACTION: "/cgi-bin/sqml/filename.sqml"
2. The names of the values being passed from an HTML form must be identical to the variable names in th SQml^TM file.
3. Variables in the SQml^TM file may not contain underscores.
4. The SQml^TM file must connect to the database in order to retrieve information. This is done in the connect tag:
   

    <sql.connect userid="username/passwd@t:computername">
   

5. Variables created by the SQml^TM cursor may only be used between the beginning of that cursor and that cursor's end tag. The information retrieved cannot be seen outside these boundaries.
6. While inside the cursor tag, variables are preceded by a colon (Example: ":variable"). While outside the tag, variables are preceded by an (&) and followed by a (;) (Example: "&variable;").

   Try These Demo Examples

   Below are some examples of forms that send data to SQml^TM files. Each form contains a link to a copy of the SQml^TM file that processes the information. I recommend viewing the SQml^TM source both before you submit and after you have seen the output. The SQml^TM material is in red and the comments explaining the SQml^TM code are in grey. In some of the examples I have numbered the cursors for clarity. These numbers are not in the actual script. You should also helpful to view the source for the HTML form by clicking the top of your browser: first on View, then on Document Source.

   Practice 1: In this example, the value that names a product line is passed from an HTML form to an SQml^TM file. The value passed is inserted into a SQml^TM iterative cursor (<sql.iter>). Specifically, the value is inserted into the cursor's where clause so the value may be used to narrow the database query. The data retrieved will represent only the product line that was chosen in the HTML form. The data retrieved is assigned to variables in the into statement. After the values have been assigned to variables, they are used in the document.

   The <sql.iter> cursor acts like cursors in most languages. It releases the information retrieved by the select statement one row at a time. Each row retrieved is used to fill in the document's variable values. The cursor loops until it is empty.

   Practice 2: In this example, three values are passed from an HTML form. We still use the value which names a product line. The two new values represent the low number and high number in a price range. They are all used in the where clause to narrow the search.

   Practice 3: This example uses four variables sent from an HTML form. They are the same three that were used before plus the value which describes a color. They are also inserted into the where clause. This example also shows how to get around the problem of null values by using a SQL*PLUS function. This problem occurs when a variable is not assigned a value. For instance, someone might leave a text field blank.

   Practice 4: This example is very similar to Practice 3. In fact, The HTML form is exactly the same. The difference is in the SQml^TM file that processes the information sent by the form. When you look at the SQml^TM source code, you will see two cursors. The first one is the same as it was in the last example. The second one contains a variable in its where clause. This variable was created in the first cursor's into statement. The information retrieved in the first cursor is used in the second cursor, the nested cursor. In this case, we used the value retrieved for the product's number.

   The second cursor will then retrieve information pertaining to one specific product. The second cursor selects from a different table than the first cursor. It will loop until all its rows have been used. Once the second cursor is finished, the first cursor releases another row for processing. This pattern will continue until the first cursor empties.

   Note the placement of the second cursor and its end tag (</sql.iter>). See how this placement allows the table to become either as large or as small as it needs to be?

   Customer Catalog Search: This example expands on the previous examples. The HTML form allows customers to search for products according to several different criteria. The SQml^TM file the information is sent to contains four cursors. Each cursor selects from a different table. The first and second cursors use values passed from the form in their where clauses. The third and fourth cursors use the product number retrieved by the first cursor.

   Distributor Catalog Search: This example is a lot like the Customer Catalog Search. The HTML form is a little different though. It uses check boxes. In the form we are giving the user the option to choose one or more product lines and one or more status. This data must be handled a little differently than other data we have seen used in the cursor. When you look at the SQml^TM source, notice how the parentheses are placed in the where clause.

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