Limit rows using Table
I have never tried it on a table field, but you could try:

{% for row in block.example.limit('1').order('RAND()') %}
    {{ row.examplerow }}
{% endfor %} 


OK, above will not work. I went back on my theory and actually tried it on a table field I had laying around. This worked for me:

{% set rows = shuffle(block.example) %}

{% for row in rows | slice(0, 1) %}
   {{ row.examplerow }}
{% endfor %}