Couple of minor tweaks to the information you provided here, When you say count(1) you are actually using a row ordinal in this case not a numeric value as you state. for example select count(1) from USER_TABLES; selects the nonnull values in the first row and returns that count. select count(2) from USER_TABLES; selects the nonnull values in the second row and returns that count. otherwise this second query would return a number twice as large as the first query. Your performance tuning tip does have one more issue, it is true that in MSSQL the count(1) vs Count(*) will give a better performance in the 1st scenario, However in Oracle even if you were to use count(0) (which would use the virtual rownum column) the execution plan would be the exact same for all of these PLSQL statements.
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