我有这样的数据:
+---------------+------+
| timestamp | robo |
+---------------+------+
| 1518259341785 | A |
| 1518259341785 | A |
| 1518259341785 | A |
| 1518259341785 | RE |
+---------------+------+
还有这个:
+---------------+------+
| timestamp | robo |
+---------------+------+
| 1518259341788 | RE |
| 1518259341788 | RE |
| 1518259341788 | RE |
| 1518259341788 | A |
+---------------+------+
众所周知，如果我们对数据进行分组并计算行数，使用以下 SQL:
SELECT timestamp, robo, COUNT(*) AS num_rows
FROM tables
GROUP BY timestamp
num_rows 将是 4。如何根据条件 only if robo RE = 1 在时间戳中对数据进行分组。这样 1518259341788 组就不会计数/出现。谢谢。
更新: 无条件分组结果:
+---------------+------+----------+
| timestamp | robo | COUNT(*) |
+---------------+------+----------+
| 1518259341785 | A | 4 |
| 1518259341788 | A | 4 |
+---------------+------+----------+
条件分组的预期结果:
+---------------+------+----------+
| timestamp | robo | COUNT(*) |
+---------------+------+----------+
| 1518259341785 | A | 4 |
+---------------+------+----------+
最佳答案
如果您想获得每个timestamp值的记录数，但前提是该timestamp值的RE记录数是1，那么你可以这样做:
SELECT timestamp, COUNT(*) AS num_rows
FROM tables
GROUP BY timestamp
HAVING SUM(CASE WHEN robo = 'RE' THEN 1 ELSE 0 END) = 1
关于MySQL 条件分组，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/50260982/