If convertable to a SQL level expression, return than expression.
Takes an Xbasic syntax expression and converts it to a SQL expression. If the expression cannot be converted, returns a null string.
Field names from the current active-link table that are referenced in the XbaseExpression are converted to the corresponding SQL expression. Assume that you have an active-link table. The active link table might have (say) two fields: fname and lname. The 'fname' field in the active-link table maps to a field called 'firstname' in the remote table and the 'lname' field map to a field called 'lastname' in the remote table.
t = table.open("customers") ?t.to_sql_expression("fname+lname") = "Firstname+Lastname"
In this next example, assume that the active-link table's SQL Select statement is:
SELECT firstname, lastname, concatenate(address, ' ', city, ' ', state,' ', zip) as address FROM customers.
The active-link table will have three fields: firstname, lastname and address
t = table.open("customers") ?t.to_sql_expression("address = '123 main st boston ma 02139'") = concatenate(address, ' ', city, ' ', state,' ', zip) = '123 main st boston ma 02130'
If the XbaseExpression cannot be converted to a SQL expression, a blank string is returned. Reasons why the conversion might fail include a reference to a function that has no SQL equivalent.