如何从子查询中的不同表中获取特定行数

Question

我知道这是可能的，但我没有足够的经验来知道如何进行子查询。
情况是这样的：

Table 1:
+--------------------+--------------------+
|               v_id |             v_name |
+--------------------+--------------------+
|                  1 |            v_name1 |
+--------------------+--------------------+
| etc...

Table 2:
+--------------------+--------------------+
|               a_id |             a_name |
+--------------------+--------------------+
|                  1 |            a_name1 |
+--------------------+--------------------+
| etc...

Table 3:
+--------------------+--------------------+
|               v_id |               a_id |
+--------------------+--------------------+
|                  1 |                  1 |
+--------------------+--------------------+
|                  1 |                  2 |
+--------------------+--------------------+
|                  1 |                  3 |
+--------------------+--------------------+
|                  2 |                  3 |
+--------------------+--------------------+
|                  2 |                  1 |
+--------------------+--------------------+

我相信这是一种很常见的情况。
因此，我在表 1 和表 2 中有独特的条目。
我想要SELECT来自Table 1的所有行并获取（作为每行的最后一个单元格）具有Table 3中相应值的行数代码>.

这是行不通的：

SELECT t1.* , COUNT(SELECT t3.* FROM  `table_3` t3 WHERE t3.v_id = t1.v_id) as entries
FROM  `table 1` t1;

我确信这里的专家会告诉我这都是错误的，但坦率地说，这就是我正在寻找的（以及一些有用的解决方案！）。 ;)

Answer 1

使用：

   SELECT t1.*,
          COALESCE(x.num_rows, 0) AS entries
     FROM `table 1` t1
LEFT JOIN (SELECT t3.v_id,
                  COUNT(*) 'num_rows'
             FROM `table_3` t3
         GROUP BY t3.v_id) x ON x.v_id = t1.v_id

Answer 2

SELECT t1.* , (SELECT COUNT(*) FROM  `table_3` t3 WHERE t3.v_id = t1.v_id) as t3Count as entries 
FROM  `table 1` t1; 

Answer 3

SELECT T1.v_id, COALESCE(COUNT(T3.v_id), 0)
FROM Table1 AS T1
LEFT JOIN Table3 AS T3
ON T1.v_id = T3.v_id
GROUP BY T1.v_id