title: Using SQL to compare counts of identifiers from two tables
body: <p>I'm trying to construct a query that compares two tables with identical structure</p>
  
  <pre><code>Table 1:
  ID | Data 
  
  Table 2:
  ID | Data
  </code></pre>
  
  <p>ID is a nonunique key (Data is repeatable but ID|Data combos are unique). I need a list of IDs where the  COUNT of those IDs is greater in Table 2 than in Table 1.</p>
  
  <p>So for example, if </p>
  
  <pre><code>Table 1
  a | data
  a | data1    
  b | data2
  
  Table 2
  a | data
  a | data1
  b | data2
  b | data3
  </code></pre>
  
  <p>would generate the output "b"</p>
  
  <p>This feels like it should be easy, but my head is scrambled right now. I'm doing this in mysql if that affects options.</p>