Question

我有这两张桌子：

table "libs"
|lib_id|name |
|1    |lib01|
|2    |lib02|
|3    |lib03|
|4    |lib04|
|5    |lib05|

table "req_libs"
|lib_id|req_lib_id|
|2     |3         |
|2     |4         |
|4     |3         |
|5     |3         |
|5     |1         |

我应该发出哪些SQL查询才能获得以下结果？

获取lib02所需的所有库的名称。预期结果：lib03，lib04
获取使用lib03的所有库的名称。预期结果：lib02，lib04，lib05

Answer 1

您可以这种方式使用INNER JOIN：

select t3.*
from libs t1
inner join req_libs t2 on t1.lib_id = t2.lib_id
inner join libs t3 on t2.req_lib_id = t3.lib_id
where t1.name = 'lib01';

Answer 2

<强> 1。获取lib02所需的所有库的名称。预期结果：lib03，lib04

SELECT t3.name
FROM libs t1
INNER JOIN req_libs t2 ON t1.lib_id = t2.lib_id
INNER JOIN libs t3 ON t2.req_lib_id = t3.lib_id
WHERE t1.name = 'lib02';

<强> 2。获取使用lib03的所有库的名称。预期结果： lib02，lib04，lib05

SELECT libs.name 
FROM libs
WHERE libs.lib_id IN (
SELECT req_libs.lib_id
FROM libs, req_libs
  WHERE libs.name = 'lib03'
  AND libs.lib_id = req_libs.req_lib_id
);

SqlFiddle：http://sqlfiddle.com/#!9/2731df/18

寻找正确的SQL查询

2 个答案: