Question

What’s a good and simple way to select from multiple tables and just order everything by date, newest to oldest?

 mysql_query("
               SELECT * 
               FROM posts, comments, photos 
               WHERE userID='$session' 
               ORDER BY date");

if I wanted to do something like that.

Answer 1

To use an ORDER BY or LIMIT clause to sort or limit the entire UNION
result, parenthesize the individual SELECT statements and place the
ORDER BY or LIMIT after the last one. The following example uses both
clauses:

(SELECT a FROM t1 WHERE a=10 AND B=1) UNION 
(SELECT a FROM t2 WHERE a=11 AND B=2) 
ORDER BY a LIMIT 10;

A statement without parentheses is equivalent to one parenthesized as
just shown.

This kind of ORDER BY cannot use column references that include a
table name (that is, names in tbl_name.col_name format). Instead,
provide a column alias in the first SELECT statement and refer to the
alias in the ORDER BY. (Alternatively, refer to the column in the
ORDER BY using its column position. However, use of column positions
is deprecated.)

-> http://dev.mysql.com/doc/refman/5.0/en/union.html