MySQL GROUP_CONCAT和PHP解析

Question

样品表

+---------+-------------------------------------+-------------+---------+--------+--------+------------+----------+---------+------------+
| book_id | book_name                           | isbn_no     | cate_id | aut_id | pub_id | dt_of_pub  | pub_lang | no_page | book_price |
+---------+-------------------------------------+-------------+---------+--------+--------+------------+----------+---------+------------+
| BK001   | Introduction to Electrodynamics     | 0000979001  | CA001   | AUT001 | P003   | 2001-05-08 | English  |     201 |      85.00 |
| BK002   | Understanding of Steel Construction | 0000979002  | CA002   | AUT002 | P001   | 2003-07-15 | English  |     300 |     105.50 |
| BK003   | Guide to Networking                 | 0000979003  | CA003   | AUT003 | P002   | 2002-09-10 | Hindi    |     510 |     200.00 |
| BK004   | Transfer  of Heat and Mass          | 0000979004  | CA002   | AUT004 | P004   | 2004-02-16 | English  |     600 |     250.00 |
| BK005   | Conceptual Physics                  | 0000979005  | CA001   | AUT005 | P006   | 2003-07-16 | NULL     |     345 |     145.00 |
| BK006   | Fundamentals of Heat                | 0000979006  | CA001   | AUT006 | P005   | 2003-08-10 | German   |     247 |     112.00 |
| BK007   | Advanced 3d Graphics                | 0000979007  | CA003   | AUT007 | P002   | 2004-02-16 | Hindi    |     165 |      56.00 |
| BK008   | Human Anatomy                       | 0000979008  | CA005   | AUT008 | P006   | 2001-05-17 | German   |      88 |      50.50 |
| BK009   | Mental Health Nursing               | 0000979009  | CA005   | AUT009 | P007   | 2004-02-10 | English  |     350 |     145.00 |
| BK010   | Fundamentals of Thermodynamics      | 0000979010  | CA002   | AUT010 | P007   | 2002-10-14 | English  |     400 |     225.00 |
| BK011   | The Experimental Analysis of Cat    | 0000979011  | CA004   | AUT011 | P005   | 2007-06-09 | French   |     225 |      95.00 |
| BK012   | The Nature  of World                | 0000979012  | CA004   | AUT005 | P008   | 2005-12-20 | English  |     350 |      88.00 |
| BK013   | Environment a Sustainable Future    | 0000979013  | CA004   | AUT012 | P001   | 2003-10-27 | German   |     165 |     100.00 |
| BK014   | Concepts in Health                  | 0000979014  | CA005   | AUT013 | P004   | 2001-08-25 | NULL     |     320 |     180.00 |
| BK015   | Anatomy & Physiology                | 0000979015  | CA005   | AUT014 | P008   | 2000-10-10 | Hindi    |     225 |     135.00 |
| BK016   | Networks and Telecommunications     | 00009790_16 | CA003   | AUT015 | P003   | 2002-01-01 | French   |      95 |      45.00 |
+---------+-------------------------------------+-------------+---------+--------+--------+------------+----------+---------+------------+

产出

mysql> SELECT pub_id,GROUP_CONCAT(CATE_ID)
    -> FROM book_mast
    -> GROUP BY pub_id;
+--------+-----------------------+
| pub_id | GROUP_CONCAT(CATE_ID) |
+--------+-----------------------+
| P001   | CA002,CA004           | 
| P002   | CA003,CA003           | 
| P003   | CA001,CA003           | 
| P004   | CA005,CA002           | 
| P005   | CA001,CA004           | 
| P006   | CA005,CA001           | 
| P007   | CA005,CA002           | 
| P008   | CA005,CA004           | 
+--------+-----------------------+
8 rows in set (0.02 sec)

我们可以使用PHP来做到这一点，

$dbh = new PDO("mysql:host=$hostname;dbname=$db", $username, $password);  
foreach($dbh->query('SELECT pub_id,GROUP_CONCAT(cate_id)  
FROM book_mast  
GROUP BY pub_id') as $row) {  
  //Use $row['GROUP_CONCAT(cate_id)'] 
}  

现在，如果我想解析有关cate_id =类别ID的更多详细信息，是否应该在此foreach循环内执行另一个查询？ 由于我得到了类别的ID。

Answer 1

我认为使用两个查询不是一种好习惯，因为我们可以使用联接查询或通过创建表名的别名从多个表中获取数据，如果您使用直接一个查询会更好。

注意：sql内部查询应具有不同的表名，如下所示

SELECT * FROM wp_posts where ID in(select ID from abc)

对于同一张表，您可以使用php条件进行动态查询。