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    <p>To say that <code>SELECT COUNT(*) vs COUNT(1)</code> results in your DBMS returning "columns" is pure bunk. That <em>may</em> have been the case long, long ago but any self-respecting query optimizer will choose some fast method to count the rows in the table - there is <strong>NO</strong> performance difference between <code>SELECT COUNT(*), COUNT(1), COUNT('this is a silly conversation')</code></p> <p>Moreover, <code>SELECT(1) vs SELECT(*)</code> will NOT have any difference in INDEX usage -- most DBMS will actually optimize <code>SELECT( n ) into SELECT(*)</code> anyway. See the ASK TOM: Oracle has been optimizing <code>SELECT(n) into SELECT(*)</code> for the better part of a decade, if not longer: <a href="http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1156151916789" rel="noreferrer">http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1156151916789</a></p> <blockquote> <p>problem is in count(col) to count(<em>) conversion <strong></em> **03/23/00</strong> 05:46 pm *** one workaround is to set event 10122 to turn off count(col) ->count(<em>) optimization. Another work around is to change the count(col) to count(</em>), it means the same, when the col has a NOT NULL constraint. The bug number is 1215372.</p> </blockquote> <p>One thing to note - if you are using COUNT(col) (don't!) and col is marked NULL, then it will actually have to count the number of occurrences in the table (either via index scan, histogram, etc. if they exist, or a full table scan otherwise). </p> <p>Bottom line: if what you want is the count of rows in a table, use COUNT(*)</p>
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    1. POIn SQL, what’s the difference between count(*) and count('x')?
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    1. USMatt Rogish
    1. USMatt Rogish
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    1. POIn SQL, what’s the difference between count(*) and count('x')?
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    1. COIt's not correct to say there's not a difference between select(n) and select(*). If you have a covering index that includes n, you get the data straight from the leaf level of the index and don't have to go back to the table, which is much faster.
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    2. COThe DBMS optimizer *will* realize this, and choose the correct index for the job. Provided there is an index, rare is the day that I've seen a DBMS actually **count** rows on the table. Moreover, the presence of NULLs often cause semantic bugs. When you want the # of rows in a table, use COUNT(*)!!!
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