在MYSQL中查询的默认顺序是什么？

Question

mysql> explain SELECT p.id ID, p.job_desc_title Title, p.url URL, substr(p.posting_date, 1, 10) Date, 
    ->           p.job_city_name City, 
    ->           p.job_state_name State, 
    ->           b.screen_name Name, b.type Type,f.name Company,IF(g.account_id IS NULL,0,1) Online 
    ->           FROM postings p 
    ->       LEFT JOIN accounts b on p.account_id=b.id 
    ->       LEFT JOIN companies f on f.id=p.job_cmp_id 
    ->       LEFT JOIN online g ON g.account_id=p.account_id 
    ->       WHERE (MATCH(job_desc,job_desc_title,k_state,k_city,zip) AGAINST('+java' IN BOOLEAN MODE)) AND b.closed=0 AND NOT p.expired 
    ->       
    ->       LIMIT 0 , 5 
    -> ; 
+----+-------------+-------+----------+--------------------------------------------------+--------------------------------------+---------+-----------------+------+-------------+ 
| id | select_type | table | type  | possible_keys         | key         | key_len | ref    | rows | Extra  | 
+----+-------------+-------+----------+--------------------------------------------------+--------------------------------------+---------+-----------------+------+-------------+ 
| 1 | SIMPLE  | p  | fulltext | FK_listings,f_postings_city_state_desc_title_zip | f_postings_city_state_desc_title_zip | 0  |     | 1 | Using where | 
| 1 | SIMPLE  | f  | eq_ref | PRIMARY           | PRIMARY        | 4  | v3.p.job_cmp_id | 1 |    | 
| 1 | SIMPLE  | g  | eq_ref | account_id          | account_id       | 4  | v3.p.account_id | 1 | Using index | 
| 1 | SIMPLE  | b  | eq_ref | PRIMARY           | PRIMARY        | 4  | v3.p.account_id | 1 | Using where | 
+----+-------------+-------+----------+--------------------------------------------------+--------------------------------------+---------+-----------------+------+-------------+ 
4 rows in set (0.00 sec) 

它曾经是按相关性排序，但现在看来不是。

Answer 1

如果没有排序，“默认”排序将取决于查询中使用了哪些索引以及它们的使用顺序。这可能会随着数据/统计信息的变化以及优化器选择不同的计划而发生变化。

如果您想按特定顺序输入数据，请使用ORDER BY。但我相信你已经知道:)

Answer 2

不要假定一个订单，如果你需要它的顺序，使用ORDER BY子句。