Need a row count after SELECT statement: what's the optimal SQL approach?

Question

I\'m trying to select a column from a single table (no joins) and I need the count of the number of rows, ideally before I begin retrieving the rows. I have come to two app

Answer 1

Here are some ideas:

• Go with Approach #1 and resize the array to hold additional results or use a type that automatically resizes as neccessary (you don't mention what language you are using so I can't be more specific).
• You could execute both statements in Approach #1 within a transaction to guarantee the counts are the same both times if your database supports this.
• I'm not sure what you are doing with the data but if it is possible to process the results without storing all of them first this might be the best method.

Answer 2

Just to add this because this is the top result in google for this question. In sqlite I used this to get the rowcount.

WITH temptable AS
  (SELECT one,two
   FROM
     (SELECT one, two
      FROM table3
      WHERE dimension=0
      UNION ALL SELECT one, two
      FROM table2
      WHERE dimension=0
      UNION ALL SELECT one, two
      FROM table1
      WHERE dimension=0)
   ORDER BY date DESC)
SELECT *
FROM temptable
LEFT JOIN
  (SELECT count(*)/7 AS cnt,
                        0 AS bonus
   FROM temptable) counter
WHERE 0 = counter.bonus

Answer 3

You might want to think about a better pattern for dealing with data of this type.

No self-prespecting SQL driver will tell you how many rows your query will return before returning the rows, because the answer might change (unless you use a Transaction, which creates problems of its own.)

The number of rows won't change - google for ACID and SQL.

Answer 4

IF (@@ROWCOUNT > 0)
BEGIN
SELECT my_table.my_col
  FROM my_table
 WHERE my_table.foo = 'bar'
END