CHAPTER 1: Conventions

The following typographical conventions are used in this manual to aid the reader in locating and identifying information within notations. You should read this section carefully since you will need this information to understand the syntax of commands.

For the sake of brevity, system prompts and Empress prompts are not reproduced for many of the shorter examples. In the case of longer and more complex illustrations, the operating system prompt (represented as %) and the Empress SQL prompt (*) are often displayed to indicate the beginning and end of commands.

Table 1-1: Typographical Conventions - General

PAGEWIDTH 
TODAY

Table 1-2: Typographical Conventions - SQL Statements

SELECT 
DISPLAY

table 
attr

Table 1-3: Typographical Conventions - Keyboard Keys

A table can be referred to by a database name followed by a colon (:) followed by the table name (except in a PRINT statement). That is, a table can be written as:

database:table_name

A script can access tables from several databases. A SELECT statement can retrieve data from several databases.

An attribute can be referred to as:

table.attr_name

where:

Any attributes retrieved via a SELECT statement may be used later in the script as though they were variables. Wherever an attribute name appears in a script, its current value will be substituted.

Complex attribute names must be enclosed in quotes and preceded by the ATTR keyword, for example, ATTR 'job no.'. (The keyword ATTR may be omitted from the WHERE clause of a SELECT statement, but is required in the list of items selected in order to distinguish a complex attribute from an ordinary character string.)

If two attributes with the same name are retrieved from different tables, they must always be qualified by their table names when referred to later, so that Empress Report Writer can distinguish between them.

For example, number in the customers table is different from number in the hours table. If we have used a SELECT statement of the form:

SELECT customers.number, address, hours.number,
     ATTR hours, job_no
          FROM hours, customers, jobs
          WHERE customers.number = jobs.customer_no
          AND jobs.job_no = hours.number;

we must always specify customers.number or hours.number later in the report, and not just number, to be sure of getting the correct value.

Empress Report Writer supports variables which may hold character or numeric values, and which may be used and manipulated in a number of ways. Variable names may be of any length, and all characters in a variable name are significant. Names may include periods, underscores, or colons, but may not include spaces, tabs, or non-printing characters. Keywords may not be used as variable names.

Variables may be PARAMETERs or defined in LET statements. A variable is created when it is first mentioned.

For example, the statement:

LET title = "EMPLOYEES OF UNIVERSAL AUTOMOTIVE" CONCAT
     "SERVICES, APRIL 1992";

assigns the character string "EMPLOYEES OF UNIVERSAL AUTOMOTIVE SERVICES, APRIL 1992'' to a variable named title. If this variable did not previously exist, it is created. If it did already exist, its previous value is replaced. Wherever title appears later in the report, the character string "EMPLOYEES OF UNIVERSAL AUTOMOTIVE SERVICES, APRIL 1992'' will be substituted for it.

As another example, the statement:

LET nextpage = PAGENUMBER + 1;

assigns a value one greater than the current page number to a variable named nextpage.

If a variable is used in a SELECT statement the prefix var. must be placed before the variable name in order for its value to be substituted correctly. These variable names also cannot contain underscores.

If the variable employee has the current value Jones, then to select all Jones' records from the loans table, the following would be used:

SELECT FROM loans WHERE name = 'var.employee';

Note

The quotes are used because the substituted value will be a character string; a date, decimal or float variable does not need quotes.

1.4 Reserved Keywords

Empress Report Writer has a number of keywords and system variable names which may not be used as ordinary variable names. For a complete list of all reserved keywords, please refer to our Reserved Keywords document.

Any attributes which have the same name as a keyword must be treated as complex; it must be enclosed in quotes and preceded by the keyword ATTR.

The keyword NULL can be used in comparisons with attribute values to test whether or not an attribute is null. For example:

IF phone = NULL
    THEN
    PRINT "No current phone number", NEWLINE;
END;

Printing of nulls is controlled by the Empress system variable MSMWNULLOK. If this variable is set to anything, all null values will be printed as a blank field of the specified width. The variable MSMWNULLOK is set by default, so nulls are printed as blanks by default.

If the variable MSMWNULLOK is unset, an error message is printed when Empress Report Writer tries to print a NULL.

Refer to the Empress SQL: User's Guide manual for instructions on setting Empress variables.

Character strings are enclosed in single or double quotes, may contain any ASCII character except NULL (0), and are printed out exactly as they appear in the PRINT statement.

Backslashes ( \) have no special meaning, and are not used for quoting other characters. If the character string includes a quote of the same type as the delimiting quotes, this included quote must be doubled (that is, printed twice). Hence, if double quotes are used as the string delimiters, a double quote actually contained in the string must be written as "", and if single quotes are the delimiters, an included single quote must be written as ''.

Empress Report Writer character strings do not recognize the C programming language conventions for specifying new lines, tabs, backspaces, etc. Thus, "\n'' will print as the two characters "\'' and "n'', not as a new line; similarly, "\b'' is "\'' and "b'', not a backspace.

In an Empress Report Writer script, any text between "/*'' and "*/'' is considered a comment and ignored. A single comment may span several lines.