Question

我有一个mysql表，其中包含两列'test-id'和'q-id'。 'test-id'范围是1到160，test-id的每个值都有100'q-id'。

ex: test-id   q-id
    1         126    #first row
    1         134    #second row
    ...
    1         66    #hundred row

SELECT COUNT(DISTINCT `q-id`)
             from `test`
             WHERE `test-id` = 1;  #answer is 100

我想计算哪个test-id有多少q-id。如何在单个查询中执行此操作？

Answer 1

要理解的关键语句是GROUP BY语句。

SELECT "test-id", COUNT(DISTINCT "q-id") as qid_count FROM "test" GROUP BY "test-id"

Answer 2

SELECT testid, COUNT(DISTINCT q-id) from test Group by testid

对COUNT个不同行

2 个答案: