We can specify columns we want to calculate in two ways:
COUNT(*) will count all rows in all the columns. The result will be taken from the column that has the highest result.
COUNT(FIELD_NAME) that will calculate the row for a particular field (column).
Furthermore, we can use the COUNT function with or without the DISTINCT clause:
COUNT to count all the rows even if there are duplications of data.
COUNT( DISTINCT ...) to calculate unique rows (rows with same values will not be counted). You can visit my site for more details.
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