Pretty self explanatory question. Is there any reason to use one or the other?
漂亮的自我解释性的问题。有什么理由使用其中一个或另一个?
5 个解决方案
#1
46
Count(*) counts all records, including nulls, whereas Count(fieldname) does not include nulls.
Count(*)计算所有记录，包括nulls，而Count(fieldname)不包含nulls。
#2
6
Select count(*) selects any row, select count(field) selects rows where this field is not null.
选择count(*)选择任何行，选择count(字段)选择该字段不为空的行。
#3
3
If you want to improve performance (i.e. be a complete performance Nazi), you might want to do neither.
如果你想提高性能(比如，做一个完全的纳粹分子)，你可能也不想这样做。
Example:
例子:
SELECT COUNT(1) FROM MyTable WHERE ...
#4
1
This puzzled me for a while too.
这也让我困惑了一阵子。
In MySQL at least COUNT(*) counts the number of rows where every (*) value in the row is not null. Just COUNTing a column will count the number of rows where that column is not null.
在MySQL中，至少COUNT(*)计算行中每个(*)值不为空的行数。仅仅数一列就会数出列不为空的行数。
In terms of performance using a single column would be slightly faster,
就性能而言，使用单个列会稍微快一些，
#5
-1
count(*) is faster if table type is MyISAM with no WHERE statement. With WHERE the speed will be the same for MyISAM and InnoDB.
如果表类型是MyISAM，而没有WHERE语句，则count(*)更快。MyISAM和InnoDB的速度是一样的。
#1
46
Count(*) counts all records, including nulls, whereas Count(fieldname) does not include nulls.
Count(*)计算所有记录，包括nulls，而Count(fieldname)不包含nulls。
#2
6
Select count(*) selects any row, select count(field) selects rows where this field is not null.
选择count(*)选择任何行，选择count(字段)选择该字段不为空的行。
#3
3
If you want to improve performance (i.e. be a complete performance Nazi), you might want to do neither.
如果你想提高性能(比如，做一个完全的纳粹分子)，你可能也不想这样做。
Example:
例子:
SELECT COUNT(1) FROM MyTable WHERE ...
#4
1
This puzzled me for a while too.
这也让我困惑了一阵子。
In MySQL at least COUNT(*) counts the number of rows where every (*) value in the row is not null. Just COUNTing a column will count the number of rows where that column is not null.
在MySQL中，至少COUNT(*)计算行中每个(*)值不为空的行数。仅仅数一列就会数出列不为空的行数。
In terms of performance using a single column would be slightly faster,
就性能而言，使用单个列会稍微快一些，
#5
-1
count(*) is faster if table type is MyISAM with no WHERE statement. With WHERE the speed will be the same for MyISAM and InnoDB.
如果表类型是MyISAM，而没有WHERE语句，则count(*)更快。MyISAM和InnoDB的速度是一样的。