mysql - value of SELECT COUNT(DISTINCT allcolumns) bigger than SELECT COUNT(1) -


i run following sql in mysql, , why 2 count show different results?

select count(1), count(distinct column1, column2, column3, column4, column5) distinctcount `parts_color`;

the results are:

  • count(1): 647611
  • distinctcount: 647263

why?

your table parts_color must have duplicate values.

select count(1) similar select count(*) retains duplicate values , returns count.

when use distinct in query duplicate values discarded , hence value less count(1).


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