Ответ на пост «Задачи с собеседования по SQL»⁠⁠1

Example Answer Structure

Question: What value will the following query return?

SELECT COUNT(*) FROM TMP_TABLE;

Answer:

To determine the result of the query SELECT COUNT(*) FROM TMP_TABLE;, we need to understand what the COUNT(*) function does in SQL. The COUNT(*) function counts the number of rows in a table, regardless of whether they contain NULL values or not.

Let's look at the data in the table TMP_TABLE:

column1column21212NULL131214NULLNULL1315

There are 5 rows in the table. The COUNT(*) function will count all these rows, including those with NULL values.

Therefore, the query:

SELECT COUNT(*) FROM TMP_TABLE;

will return the value 5.

This value is the total number of rows in the table TMP_TABLE, without any consideration of the content of the columns or whether they contain NULL values.
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