title: Check if a string contains only number
body: <p>I am trying to check if a <code>string</code> contains only valid number in the following format</p>
  
  <pre><code>123.456
  123
  .356
  </code></pre>
  
  <p>But it should reject anything that contains non-numbers including double dots. Here are some invalid formats</p>
  
  <pre><code>d123.456
  123d
  12d3
  d.1256
  12d.456
  12.d12
  12.d45d
  12.45.56
  </code></pre>
  
  <p>I have done the following</p>
  
  <pre><code>SELECT CASE WHEN '123.00' NOT LIKE '%[^0-9.]%' THEN 'Valid' ELSE 'Invalid' END
  </code></pre>
  
  <p>When seems to work except for the case where there is more than one dot in the string.</p>
  
  <p>How can I tweak the regular expression to only allow one dot otherwise return 'Invalid'?</p>