scalar variable support for matches regex

[Patrick Naughton]

The following example shows how the binary operator == works with a scalar variable as the right hand side.

datatable(a: string, b: string) [ 
"foo", "blah*",
"bar", "ba*",
"same", "same"
] | where a == b

This works fine and returns the "same", "same" row...

Why doesn't the matches regex operator work the same way?

datatable(a: string, b: string) [ 
"foo", "blah*",
"bar", "ba*",
"same", "same"
] | where a matches regex b

I would have expected it to return the "bar", "ba*" row.

Instead it says:

SYNTAX ERROR
matches regex: failed to cast argument 2 to scalar constant
Support id: a11422a7-01b7-486b-84f1-e7473be0e164

[#2]

Hi Patrick,

The argument to 'matches regex' is a constant as the error message says. This is in order to ensure that the predicate is not calculated for each row something that will result in a very poor performance. 

Thanks,

Avner