Advantage SQL Engine
The DECLARE statement is used to declare variables and cursors.
DECLARE variable_declaration | cursor_declaration [, … ];
variable_declaration ::= variable_name variable_type
cursor_declaration ::= cursor_name CURSOR [ AS cursor_statement ]
cursor_statement ::= select_statement | execute_statement
All variables used in the script must be declared at the beginning of the script using one or more DECLARE statements. The Advantage Query Engine will perform type checking on variables when they are used in assignments or expressions. All variables are initialized to NULL when declared.
A cursor is not accessible until it is opened using the OPEN statement. Once a cursor is open, the column values in the cursor can be accessed using the dot notation: cursorname.columnname.
Variable and cursor names are case insensitive and cannot be a reserved keyword or a quoted identifier.
Although the Advantage SQL Engine does not require variable names to be in any specific format, the special character '@' may be used as the first character of a variable name to avoid potential conflicts between column names and variable names in SQL statements. The following sample script will illustrate the problem:
DECLARE empid Integer;
empid = 1;
UPDATE employees SET ManagerID = empid WHERE branch = 'R&D';
The intention of the script is to change the manager for all R&D branch employees to employee number 1. However, if there is a column named 'empid' in the table, which is a very likely scenario, the usage of the "empid" in the SET clause will be ambiguous. It can reference either the 'empid' column in the table or the variable empid. In case of this type of ambiguity, the error code 2229, ambiguous reference, will be returned.
To avoid this type a problem, the variable names in the SQL scripts should be declared with '@' as the first character. When the SQL engine encounters a name that begins with the '@' character, it will attempt to resolve it into a variable reference. If the name can be resolved into a variable reference, there will be no addition attempt to check for conflict with a column name. In other words, the 2229 error will never occur when using variable names that begin with the '@' character. Using this approach, the sample script above could be written as:
DECLARE @empid Integer;
@empid = 1;
UPDATE employees SET ManagerID = @empid WHERE branch = 'R&D';
The variable_type can be any supported data type with the exception of the AUTOINC type. In addition, STRING is a valid type that can be used to declare a variable length string. A STRING type variable is different from a CHAR(n) type variable in the following aspects:
· When string data is assigned to a CHAR(n) variable, the resultant string is always n characters long. If the source string is longer, it is truncated to n characters. If the source string is shorter than the CHAR(n) variable, the resultant string is padded with spaces to a length of n.
· When string data is assigned to a STRING variable, no padding or truncation will be performed. STRING variables can grow to any length, limited only by the resources available on the machine.
DECLARE strLocal String;
DECLARE iLocal Integer, jLocal Integer;
DECLARE cLocal Char(20), Cursor1 Cursor, Cursor2 Cursor AS SELECT * FROM employees;
WHILE FETCH Cursor2 DO
iLocal = Cursor2.empid;