How To Select The Same Field From Two Tables In One Query
| Computing : Learning PHP If you are using mySQL often then there are various scenarios you will come across at one time or other. One of these will be wanting to collect the same field from two tables in one query. For instance, imagine that in a forum the first post is stored in a separate table to the replies. Both have a date_posted column. Now if you want to find the latest post for a forum, you will need to sort in descending order limit 1 the Combined data from those two fields - as a new post may be the latest post or a reply to any existing post. To do this easily, you can use the UNION query in mysql. Thus the relevant query here would be: SELECT date_posted FROM newposts UNION SELECT date_posted FROM replies ORDER BY date_posted DESC LIMIT 1 You simply stitch the two calls to select with the keyword UNION in between (requires mySQL 4).
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