In the previous version, we use explain SQL command to see the specific implementation plan. In the new version of MySQL 8.0.18 expand explain, one is explain format = tree, and the other is based explain format = tree extending extension Explain Analyze, today we look at how the command is executed.
Or do the testing sbtest1 table.
explain analyze select count(*) from sbtest1;
This result is very curious, where without conditions, and consequently can not show up, looks like a BUG?
Too, add where id> 0 and try again.
explain analyze select count(*) from sbtest1 where id>0;
Note the red underlined parts within it will run the query and measure the execution time.
Meaning explain:
1) rows cost part = 4,936,262, and the results are consistent explain generation, estimating the number of lines are read.
2) Actual rows part = 10000000, the real results of this execution is returned by SQL, see as shown below
3) actual time = 62004.565 (in ms milliseconds), this is converted into a second SQL execution time is 62 seconds, but in fact there is a great error, you see above
The execution time of 7.98 seconds, it is rounded to 8 seconds, 62/8 about the error reached about 77%, so we can not really believe these numbers.