What does select count (1) mean?

Count (1) is actually to calculate the total number of qualified rows. 1 does not represent the first field, but a fixed value. In fact, you can think of such a field in the table. This field is a fixed value of 1, count (1), that is, to calculate the total number of 1. similarly, count (2) can also be obtained. The obtained values are exactly the same. Count ('x') and count ('y') can be used. The same understanding. You can use this statement, and the returned values are the same. Is the count. Count (*). During execution, the asterisk is translated into the specific name of the field, and the effect is the same. However, an additional translation action is less efficient than a fixed value.

What does select count (1) mean?