我应该使用UNION还是其他方式从多个表中选择数据？

Question

I have two tables in my mysql database: female and male . They both have 3 columns each: id , name and age . I want a html table to be displayed with both table's data in it.

I have these code pieces:

$result = mysql_query("SELECT * FROM female ORDER BY age DESC LIMIT 20");
while($row = mysql_fetch_array($result))
{
  $age = $row['age'];
  $name = $row['name'];
}

and

$result01 = mysql_query("SELECT * FROM male ORDER BY age DESC LIMIT 20");
while($row01 = mysql_fetch_array($result01))
{
  $age01 = $row01['age'];
  $name01 = $row01['name'];
}

So how should I mix these tables (the data)? Should I use the mysql UNION function or something else? What is the appropriate code for this job?

Thanks...

Answer 1

You should use

SELECT * FROM female ORDER BY age DESC LIMIT 20
UNION
SELECT * FROM male ORDER BY age DESC LIMIT 20

or

SELECT * FROM
    (SELECT * FROM female
     UNION
     SELECT * FROM male)
ORDER BY age DESC LIMIT 20

Finally, a consideration: why do you use separate tables for males and females? You caould use a single table with a column for sex...

Answer 2

Well, the most appropriate solution is to not have separate male and female tables, but rather to have one people table with a gender column. That way, you don't have to go messing around with unionizing tables and going crazy to merge them when, really, all these rows belong in the same table. After all, if you're really all that interested in selecting only male or female people, that's what WHERE is for.

But if this is a legacy database with the schema set in stone, I feel your pain, and Marco's solution would do the trick :)