我有一个 sql 查询错误

Question

Error is : Every derived table must have its own alias is there any error?

$sql = "SELECT r_name FROM(
                          SELECT b.r_name,a.check_in,a.check_out
                          FROM rooms b, bookings a
                          WHERE b.r_name = a.r_name )
                   WHERE(
                          check_in <= CAST($mychickIn AS DATETIME) AND check_out >= CAST($mychickIn AS DATETIME)
                          OR check_in < CAST($mycheckOut AS DATETIME) AND check_out >= CAST($mycheckOut AS DATETIME)
                          OR check_in >= CAST($mychickIn AS DATETIME) AND check_out <= CAST($mycheckOut AS DATETIME))
  ";

Answer 1

You have to give the table, which you have created with the SELECT in the FROM case, a alias. To access a "table" created in the FROM, it needs a name.

Try something like this:

$sql = "SELECT t.r_name FROM(
                      SELECT b.r_name,a.check_in,a.check_out
                      FROM rooms b, bookings a
                      WHERE b.r_name = a.r_name ) t
               WHERE(
                      t.check_in <= CAST($mychickIn AS DATETIME) AND t.check_out >= CAST($mychickIn AS DATETIME)
                      OR t.check_in < CAST($mycheckOut AS DATETIME) AND t.check_out >= CAST($mycheckOut AS DATETIME)
                      OR t.check_in >= CAST($mychickIn AS DATETIME) AND t.check_out <= CAST($mycheckOut AS DATETIME))";

Answer 2

It is nested selection statement, and inner select results are put in temporary table. You should name temporary table explicitly.

select * from (select * from t) should be changed to 
select * from (select * from t) as t_tmp;