mysql select 计算多个条件

Question

我有一个包含元素的 table。

每个元素都有其父元素instance_id，一个number_of_lines的代码，和 deletion_date 删除时。

我构建了一个查询，用于计算按实例分组的元素以及具有代码的元素（number_of_lines 非零）和已删除的元素（deletion_date 非空）

SELECT instance_id, 
    COUNT(id) AS elementsfound,
    COUNT(NULLIF(number_of_lines,0)) AS havecode,
    (COUNT(id)-COUNT(NULLIF(number_of_lines,0))) AS havenocode,      
    COUNT(deletion_date) AS beenremoved,          
    (COUNT(id)-COUNT(deletion_date)) AS stillexistent        
  FROM elements        
  GROUP BY instance_id

我得到了一个正确的结果（缩写）

+-------------+---------------+----------+------------+-------------+---------------+
| instance_id | elementsfound | havecode | havenocode | beenremoved | stillexistent |
+-------------+---------------+----------+------------+-------------+---------------+
|          59 |         93123 |    24109 |      69014 |       45397 |         47726 |
|          69 |         46399 |     7837 |      38562 |       23929 |         22470 |
|          71 |         41752 |     8746 |      33006 |        6960 |         34792 |
|          75 |         29097 |     4303 |      24794 |       13670 |         15427 |
|          77 |         41681 |     9858 |      31823 |       10540 |         31141 |
|          79 |         17800 |      695 |      17105 |       13391 |          4409 |
|          82 |         25323 |     2481 |      22842 |       20914 |          4409 |
|          83 |         12831 |     2544 |      10287 |        2988 |          9843 |

...

现在，我想添加一个列，其中包含每个实例的元素数量，两者仍然存在（deletion_date 为空）and 有代码（number_of_lines 不同于零）

我找不到添加多列的 NULLIF 或 CASE WHEN 的方法。

如何包含多列条件计数器？

Answer 1

你想做什么？

sum( if(deletion_date is null and number_of_lines!=0, 1, 0) )

Answer 2

我假设你的意思是仍然存在的记录应该有 deletion_date NULL。

试试这个：

SELECT instance_id, 
    COUNT(id) AS elementsfound,
    COUNT(NULLIF(number_of_lines,0)) AS havecode,
    (COUNT(id)-COUNT(NULLIF(number_of_lines,0))) AS havenocode,      
    COUNT(deletion_date) AS beenremoved,          
    (COUNT(id)-COUNT(deletion_date)) AS stillexistent,
    COUNT(IF(deletion_date IS NULL AND number_of_lines > 0, 1, NULL)) existentwithcode
  FROM elements        
  GROUP BY instance_id

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