Indeed, the time to fetch information from a repository — be it a file or database server — far exceeds the lapse required to compile and perhaps even execute a PHP program.
After the FETCH, the program does "before and after" checking to see if anything on the row was changed by a different user while our user was staring at the screen display.
FETCH之后，程序进行“前后”检查，来查看在进行屏幕显示时，是否有不同用户对该行做了改动。
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You may be wondering why the program did not put selb and STQD in the same fetch group.