Allow lexicographical comparison of strings

AMQP SQL spec:
"The left operand is of greater value than the right operand if:
... both operands are of type string or of type symbol (any combination is permitted) and the
lexicographical rank of the left operand is greater than the lexicographical rank of the right operand."

In contrast, in JMS:
"String [...] comparison is restricted to = and <>."

Author: ansd

deps/rabbit/src/rabbit_amqp_filter_sql.erl

@@ -180,20 +180,23 @@ eval0({'like', Expr, {pattern, Pattern}}, Msg) ->
 %% "Comparison or arithmetic with an unknown value always yields an unknown value."
 compare(_Op, Left, Right) when Left =:= undefined orelse Right =:= undefined ->
     undefined;
-%% "Only like type values can be compared.
-%% One exception is that it is valid to compare exact numeric values and approximate numeric values.
-%% String and Boolean comparison is restricted to = and <>."
+%% "Only like type values can be compared. One exception is that it is valid to
+%% compare exact numeric values and approximate numeric values"
 compare('=', Left, Right) ->
     Left == Right;
 compare('<>', Left, Right) ->
     Left /= Right;
-compare('>', Left, Right) when is_number(Left) andalso is_number(Right) ->
+compare('>', Left, Right) when is_number(Left) andalso is_number(Right) orelse
+                               is_binary(Left) andalso is_binary(Right) ->
     Left > Right;
-compare('<', Left, Right) when is_number(Left) andalso is_number(Right) ->
+compare('<', Left, Right) when is_number(Left) andalso is_number(Right) orelse
+                               is_binary(Left) andalso is_binary(Right) ->
     Left < Right;
-compare('>=', Left, Right) when is_number(Left) andalso is_number(Right) ->
+compare('>=', Left, Right) when is_number(Left) andalso is_number(Right) orelse
+                                is_binary(Left) andalso is_binary(Right) ->
     Left >= Right;
-compare('<=', Left, Right) when is_number(Left) andalso is_number(Right) ->
+compare('<=', Left, Right) when is_number(Left) andalso is_number(Right) orelse
+                                is_binary(Left) andalso is_binary(Right) ->
     Left =< Right;
 compare(_, _, _) ->
     %% "If the comparison of non-like type values is attempted,

deps/rabbit/test/amqp_filter_sql_unit_SUITE.erl

@@ -123,15 +123,21 @@ comparison_operators(_Config) ->
     %% Greater than
     true = match("weight > 3", app_props()),
     false = match("weight > 5", app_props()),
+    true = match("country > 'DE'", app_props()),
+    false = match("country > 'US'", app_props()),
 
     %% Less than
     true = match("weight < 10", app_props()),
     false = match("weight < 5", app_props()),
+    true = match("country < 'US'", app_props()),
+    false = match("country < 'DE'", app_props()),
 
     %% Greater than or equal
     true = match("weight >= 5", app_props()),
     true = match("weight >= 4", app_props()),
     false = match("weight >= 6", app_props()),
+    true = match("country >= 'UK'", app_props()),
+    true = match("country >= 'DE'", app_props()),
     %% "Only like type values can be compared. One exception is that it is
     %% valid to compare exact numeric values and approximate numeric value"
     true = match("weight >= 5.0", app_props()),
@@ -149,8 +155,11 @@ comparison_operators(_Config) ->
     false = match("weight <= 4", app_props()),
     true = match("price <= 10.6", app_props()),
     false = match("price <= 10", app_props()),
+    true = match("country <= 'US'", app_props()),
+    true = match("country <= 'UK'", app_props()),
+    false = match("country <= 'DE'", app_props()),
 
-    %% "String and Boolean comparison is restricted to = and <>."
+    %% "Boolean comparison is restricted to = and <>."
     %% "If the comparison of non-like type values is attempted, the value of the operation is false."
     true = match("active = true", app_props()),
     true = match("premium = false", app_props()),
@@ -160,19 +169,15 @@ comparison_operators(_Config) ->
     false = match("premium >= 0", app_props()),
     false = match("premium <= 0", app_props()),
 
-    false = match("country >= 'UK'", app_props()),
-    false = match("country > 'UA'", app_props()),
-    false = match("country >= 'UA'", app_props()),
-    false = match("country < 'UA'", app_props()),
-    false = match("country <= 'UA'", app_props()),
-    false = match("country < 'UL'", app_props()),
-    false = match("country < true", app_props()),
-
     false = match("weight = '5'", app_props()),
     false = match("weight >= '5'", app_props()),
     false = match("weight <= '5'", app_props()),
+    false = match("country <= true", app_props()),
+    false = match("country >= true", app_props()),
     false = match("country > 1", app_props()),
-    false = match("country < 1", app_props()).
+    false = match("country >= 1", app_props()),
+    false = match("country < 1", app_props()),
+    false = match("country <= 1", app_props()).
 
 arithmetic_operators(_Config) ->
     %% Addition