1440. Evaluate Boolean Expression

Select e.left_operand, e.operator ,e.right_operand,
case when   e.operator = '>' and v1.value > v2.value  then 'true'
when  e.operator = '<' and v1.value < v2.value then 'true'
when  e.operator = '=' and v1.value = v2.value then 'true'
else 'false'
end  as value
from Expressions e  
left join variables v1 on v1.name=e.left_operand
left join variables v2 on v2.name=e.right_operand