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What Is the Difference Between Count(*) And Count(2) In Oracle?

2 minutes read

In Oracle, the COUNT() function is used to count the number of rows in a table, regardless of the presence of null values. On the other hand, the COUNT(2) function also counts the number of rows in a table but it counts all non-null values in the specified column (in this case, the column with the value 2). So, the main difference is that COUNT() counts all rows, while COUNT(2) counts non-null values in the specified column.


Can count(*) be used in subqueries in Oracle?

Yes, in Oracle, the COUNT(*) function can be used in subqueries. This can be useful in a variety of scenarios where you need to count the number of rows in a subquery result set. For example:

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SELECT 
    (SELECT COUNT(*) FROM table_name WHERE condition) AS total_count
FROM dual;


In this example, the subquery is counting the number of rows in the "table_name" table that meet a certain condition. The result of the subquery is then returned as "total_count".


Can count(*) be used with a specific column in Oracle?

No, COUNT(*) does not allow us to specify a specific column in Oracle. It will count all rows in a table regardless of any specific column. If you want to count the number of non-null values in a specific column, you can use COUNT(column_name) instead.


Are there any limitations to using count(*) in Oracle?

Yes, there are some limitations to using COUNT(*) in Oracle:

  1. COUNT(*) counts all rows, including NULL values, which may not always be desirable.
  2. For very large tables, using COUNT(*) can be resource-intensive and slow down query performance.
  3. COUNT(*) may not always give accurate results if there are duplicate rows or if the table has been updated but not committed.
  4. When using COUNT(*) with GROUP BY or DISTINCT clauses, it may not give the expected results as it counts all rows before applying the grouping or distinct operation.
  5. Using COUNT(*) on a table with a high number of rows can lead to resource contention and block other transactions.


What is the syntax for using count(*) in Oracle?

The syntax for using count(*) in Oracle is:

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SELECT COUNT(*)
FROM table_name;


In this syntax, replace table_name with the name of the table from which you want to count the rows.

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