命名临时表上的SQL语法错误

Question

Could anyone give me a hint, why the following query throws a syntax error?

SELECT *  
  FROM 
     (
       ( SELECT cu.ID id
              , name
              , ego_id
              , u.fb_id 
           FROM contact_users cu 
           JOIN users u 
             ON cu.ego_id = u.ID
       ) temp 
    LEFT 
    JOIN fb_user 
      ON temp.fb_id = fb_user.user_fb_id
     ) T4

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds 
to your MySQL server version for the right syntax to use near 'T4'...

If I remove T4 everthing is fine.

I am using MySQL 5.5.47

Answer 1

Why the following query throws a syntax error?

Because you can't alias an inline view if one doesn't exist.

When you remove T4, the engine just see's ()'s for order of operation. When you add the alias it assumes a well formed inline view exists and thus looks for the proper syntax (At least SELECT and FROM) which do not exist.

Put simply:

The alias T4 has no select or from; to resolve this:

• add them
• remove the initial ( and the Ending ) T4 (they are not needed)
• refactor the SQL (why the inline view in the first place? it's not needed.)

MORE DETAIL

Your Temp alias works because it is a complete and accurate query that can run on it's own.

SELECT cu.ID id
              , name
              , ego_id
              , u.fb_id 
           FROM contact_users cu 
           JOIN users u 
             ON cu.ego_id = u.ID

WHERE AS:

( SELECT cu.ID id
          , name
          , ego_id
          , u.fb_id 
  FROM contact_users cu 
  JOIN users u 
    ON cu.ego_id = u.ID
) temp 
LEFT 
JOIN fb_user 
  ON temp.fb_id = fb_user.user_fb_id

Is not a complete and accurate SQL statement to generate a result set. As You can see this is missing keywords 'SELECT' and 'FROM'. I suppose you could eliminate the left join and it would work but I don't think that would meet result in the desired results.

By eliminating the T4, the engine isn't attempting to parse the data between the ()'s as a valid SQL statement, instead it just see's the ()'s as order of operation and since the () don't matter on the outer portion the engine doesn't perceive a syntax error.

Answer 2

Either have Query 1 or Query 2

Query 1

SELECT * 
FROM 
    (
        SELECT * 
        FROM 
            (
                SELECT cu.ID as id, name, ego_id, u.fb_id 
                FROM contact_users as cu 
                JOIN users as u 
                 ON cu.ego_id = u.ID
            ) temp 
        LEFT OUTER JOIN fb_user 
            ON temp.fb_id = fb_user.user_fb_id
    ) T4

Query 2

SELECT cu.ID as id, name, ego_id, u.fb_id, fb_user.* 
FROM contact_users as cu 
JOIN users as u 
 ON cu.ego_id = u.ID 
LEFT OUTER JOIN fb_user 
 ON u.fb_id = fb_user.user_fb_id

I prefer Query 2