Is there a difference between the following queries, assuming there is a primary field 'id' in the table (as in speed, etc)?
SELECT COUNT(id)
FROM table
vs.
SELECT COUNT(*)
FROM table
asked Nov 8, 2009 at 16:56
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Have a look at Count(*) vs Count(col) at www.mysqlperformanceblog.com, they discuss this topic for various 'col' types (NOT NULL or not, with index, etc) and this for MyISAM and InnoDB tables.– Pascal ThiventCommented Nov 8, 2009 at 17:02
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You can look onto these threads stackoverflow.com/questions/1221559/count-vs-count1 stackoverflow.com/questions/433913/… stackoverflow.com/questions/59294/…– Rakesh JuyalCommented Nov 8, 2009 at 17:02
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2 Answers
One important different is that Count(*) and Count($col_name) can show different outputs if the $col_name column is nullable, since null values don't get counted by Count.
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2I think the question refers to the PK when it says "id", so NOT NULL is assumed, as well as a PRI index. Commented May 12, 2019 at 9:41
I know this is several years old but I don't see any evidence on which one to use, so I will post here my findings.
Executing explain in MySql Workbench for an InnoDB table on MySql 5.7 I see the following:
As you can see, both results are identical, so for this scenario both expressions are equivalent
