View the original community article here
Last tested: Aug 17, 2020
If you don't mind editing the model then here is a solution where setting the filter value to "Yes" will apply the filter rules, and setting it to anything else will just not do any filtering:
filter: apply_equality_filter { type: yesno sql: CASE WHEN {% parameter apply_equality_filter %} = true THEN ${field1} = ${field2} ELSE 1=1 END ;;}
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