Summary: In Qlik script SET is often a better choice than LET, even when the value contains quotes.
I sometimes see the LET script statement used when SET would be syntactically easier and more readable.
A brief review: SET assigns the given parameter as-is to the variable, LET treats the parameter as an expression and assigns the evaluated result to the variable.
SET x = 1+3; // x is "1+3" LET x = 1+3; // x is "4"
I frequently see a variable assignment like this:
LET eSales='sum(Sales)';
eSales stores an expression that will be used later in charts. It could also be written (simpler in my estimation) as:
SET eSales=sum(Sales);
So far just a matter of style, but the difference becomes clear when we have quotes as part of the string, for example, “Region={‘US’}”. As LET requires a quoted string, embedded quotes require some sort of escaping. In QV10 and earlier, a common way to write this with LET would be:
LET x = 'Region={' & chr(39) & 'US' & '}';
Not real pretty. Many people carry over this style even though QV11 introduced two single quotes to represent an embedded single quote.
LET x = 'Region={''US''}';
Easier to read for sure. But I think it’s even easier with SET.
SET x = Region={'US'};
That’s it. No special escaping required, just type it as it should be. What about those quotes? Shouldn’t SET strings be enclosed in quotes?
I find the documentation on SET to be thin, but here is the rule as I understand it.
Single or Double quotes in a SET statement require no special treatment as long as they are balanced (even number of quotes).
SET x = Region={'US'},Product={'Shoe'}; // Valid
SET x = Region={"U*"},Product={'Shoe'}; // Valid
SET x = I won't go; // Invalid
If the quotes are unbalanced (odd number), then the entire string needs to be enclosed in quotes or brackets. Use double quotes if we are enclosing single quotes.
SET x = "I won't go"; SET x = [I won't go];
I always favor SET over LET unless I truly want an evaluation. An exception to this is the string “$(” which will trigger an Dollar Sign Expansion, even in SET.
-Rob
For more on character escaping in Qlik from HIC see https://community.qlik.com/blogs/qlikviewdesignblog/2015/06/08/escape-sequences
