mysql更新。 count，列为null的行以及列是相同的

Question

我想更新表中的所有行，其中包含与where子句具有相同值的行数。

  

SQL

//This gives me the rows I want to update    
SELECT file1 FROM database.TableName where file2 is null
//From there I want to count all the rows that are the same
SELECT Count(*) FROM database.TableName where file1 = resulted value
//And then I want to update the row

  

我当前的查询看起来像这样

UPDATE database.TableName AS A 
SET refCount = (SELECT Count(*) 
FROM database.TableName AS B 
WHERE A.file1 = B.file1 AND A.file2 is null)    

  

表名

|ID | file1     |   file2   | refCount |
| 1 | file.txt  |           |    1     |
| 2 | file.txt  |           |    1     |
| 3 |           | file2.txt |    1     |
| 4 | file3.txt |           |    1     |

  

TableName（预期结果）

|ID | file1     |   file2   | refCount |
| 1 | file.txt  |           |    2     |
| 2 | file.txt  |           |    2     |
| 3 |           | file2.txt |    1     |
| 4 | file3.txt |           |    1     |

Answer 1

看起来你缺少更新语句的where子句。

试试这个......

UPDATE database.TableName AS A 
SET refCount = 
(SELECT Count(*) FROM database.TableName AS B WHERE A.file1 = B.file1 AND A.file2 is null)
where A.file1 = B.file1