title: MySQL update columns from table 1 based on columns on column 2 - very slow (have indexed)
body: <p>I currently have 2 tables. a 'property' table and a 'postcodelatlng' table.</p>
  
  <p>In postcodelatlng I have postcode, latitude and longitude columns. There is only 1 postcode per latitude and longitude.</p>
  
  <p>In property I also have postcode, latitude and longitude columns. There are multiple properties with the same postcode.</p>
  
  <p>I want all of my current blank latitude and longitude values in property to be updated with the correct latitude and longitude values from postcodelatlng.</p>
  
  <p>Below is what I'm currently using, but it's taking a long time. I expect it to take some time (22 million rows in property, 1.7 million in postcodelatlng)... but even after 5 minutes, I don't see ANY new latitude/longitude values in property table.</p>
  
  <p>I have indexed property (postcode, latitude, longitude) and the same for postcodelatlng.</p>
  
  <pre><code>UPDATE `property` 
  INNER JOIN `postcodelatlng` on `property`.`postcode` = `postcodelatlng`.`postcode`
  SET `property`.`latitude` = `postcodelatlng`.`latitude`, `property`.`longitude` = `postcodelatlng`.`longitude`
  </code></pre>