show variables not support mysql handlers but can use table function show_variables() to query all vars in session

Author: TCeason

tests/sqllogictests/suites/query/show_variables.test

@@ -1,24 +1,32 @@
 statement ok
 set variable (a, b) = (select 3, 'x')
 
+onlyif http
 query TTT
 show variables
 ----
 a 3 UInt8
 b 'x' String
 
+onlyif http
 query TTT
 show variables where name like 'a'
 ----
 a 3 UInt8
 
-
+onlyif http
 query TTT
 show variables where type = 'UInt8'
 ----
 a 3 UInt8
 
+onlyif http
 query TTT
 show variables where value = '\'x\''
 ----
 b 'x' String
+
+query TTT
+select name, value, type from show_variables() where name='a';
+----
+a 3 UInt8