Question

我有5个表格。新增1个初级和4个(有不同的栏目)。

objects
obj_mobiles
obj_tablets
obj_computers

这里是我的主要表格(目标)的结构。

ID ́ ́ ́ >

So what I want to do is to join objects with other (obj_mobiles,obj_tablets,...) tables, depending on type field. I know that I should use dynamic SQL. But I can t make procedure. I think it should look like something like this.

SELECT objects.type into @tbl FROM objects;
PREPARE stmnt FROM "SELECT * FROM objects AS object LEFT JOIN @tbl AS info ON object.id = info.obj_id"; 
EXECUTE stmnt;
DEALLOCATE PREPARE stmnt;

Aslo pseudo-code

SELECT * FROM objects LEFT JOIN [objects.type] ON ...

Can anyone post procedure? Also I want to have all rows not just 1 row. Thanks.

Answer 1

如果你想要所有各行(软木产出)而不是一行,那么以下各行的产出应当迅速,所有各行的产出将包含所有各栏。

Select objects.*, typestable.*
from (
    select ID as oID, "mobile" as otype, M1, M2, NULL T1, NULL T2, NULL C1, NULL C2 from obj_mobiles 
    union all
    select ID as oID, "tablet" as otype, NULL, NULL, T1, T2, NULL, NULL from obj_tablets 
    union all
    select ID as oID, "computer" as otype, NULL, NULL, NULL, NULL, C1, C2 from obj_computers) as typestable 
        left join objects on typestable.oID = objects.ID and typestable.otype = objects.type;

+------+--------------------+----------+------+----------+------+------+------+------+------+------+
| ID   | name               | type     | ID   | type     | M1   | M2   | T1   | T2   | C1   | C2   |
+------+--------------------+----------+------+----------+------+------+------+------+------+------+
|    1 | Samsung Galaxy s2  | mobile   |    1 | mobile   |    1 | Thin | NULL | NULL | NULL | NULL |
|    2 | Samsung Galaxy Tab | tablet   |    2 | tablet   | NULL | NULL | 0.98 |   10 | NULL | NULL |
|    3 | Dell Inspiron      | computer |    3 | computer | NULL | NULL | NULL | NULL | 4.98 | 1000 |
+------+--------------------+----------+------+----------+------+------+------+------+------+------+

该表如下所示。

mysql> create table objects (ID int, name varchar(50), type varchar (15));
Query OK, 0 rows affected (0.05 sec)
mysql> insert into objects values (1, "Samsung Galaxy s2", "mobile"), (2, "Samsung Galaxy Tab", "tablet"), (3, "Dell Inspiron", "computer");
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0


mysql> create table obj_mobiles (ID int, M1 int, M2 varchar(10));
Query OK, 0 rows affected (0.03 sec)
mysql> insert into obj_mobiles values (1, 0.98, "Thin");
Query OK, 1 row affected (0.00 sec)


mysql> create table obj_tablets (ID int, T1 float, T2 int(10));
Query OK, 0 rows affected (0.03 sec)
mysql> insert into obj_tablets values (2, 0.98, 10);
Query OK, 1 row affected (0.00 sec)


mysql> create table obj_computers (ID int, C1 float, C2 int(10));
Query OK, 0 rows affected (0.03 sec)
insert into obj_computers values (3, 4.98, 1000);

also to confirm the datatypes of the columns are same as the original columns, the result is saved into a table and datatypes are checked below.

create table temp_result as
Select objects.*, typestable.*
from (
    select ID as oID, "mobile" as otype, M1, M2, NULL T1, NULL T2, NULL C1, NULL C2 from obj_mobiles 
    union all
    select ID as oID, "tablet" as otype, NULL, NULL, T1, T2, NULL, NULL from obj_tablets 
    union all
    select ID as oID, "computer" as otype, NULL, NULL, NULL, NULL, C1, C2 from obj_computers) as typestable 
        left join objects on typestable.oID = objects.ID and typestable.otype = objects.type;

mysql> desc temp_result;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| ID    | int(11)     | YES  |     | NULL    |       |
| name  | varchar(50) | YES  |     | NULL    |       |
| type  | varchar(15) | YES  |     | NULL    |       |
| oID   | int(11)     | YES  |     | NULL    |       |
| otype | varchar(8)  | NO   |     |         |       |
| M1    | int(11)     | YES  |     | NULL    |       |
| M2    | varchar(10) | YES  |     | NULL    |       |
| T1    | float       | YES  |     | NULL    |       |
| T2    | int(11)     | YES  |     | NULL    |       |
| C1    | float       | YES  |     | NULL    |       |
| C2    | int(11)     | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
11 rows in set (0.00 sec)

Answer 2

如果objects is a parent table it means that objects. is a separate Object. 权利? 所有其他物品(汽车、桌子、电脑)都是物体和移动桌子的儿童,不能有同样的识别资料。如果是的话,使用这一简单问题就足够了——



SELECT * FROM objects o
  LEFT JOIN obj_mobiles m
    ON o.id = m.ID
  LEFT JOIN obj_tablets t
    ON o.id = t.ID
  LEFT JOIN obj_computers c
    ON o.id = c.ID


添加WHERE条款以过滤类型,例如:WHERE o.type = 移动。

Answer 3

USE CONCAT to create your prepare statement. eg.

@sql = CONCAT( SELECT * FROM objects AS object LEFT JOIN  , @tbl,   AS info ON object.id = info.obj_id );
PREPARE stmnt FROM @sql;
...

友情链接