???????????????????????ж???????????????????????е?WHEN-THEN?飬?????????????????????????????棬???????????е?WHEN-THEN?齫??ELSE?????????END??????????????CASE?????????????????鶼????????ELSE???????????????????????ELSE?飬???????е?WHEN-THEN?????????棬MySQL??????NULL??
????CASE??????????????????????????????????????￡?
????CASE
????????????:
????WHEN [conditional test 1] THEN [result 1]
????WHEN [conditional test 2] THEN [result 2]
????ELSE [default result]
????END
?????????????￡???????????????????????????????檔
?????????
????????????:
????mysql>SELECT CASE 'green'
????WHEN 'red' THEN 'stop'
????WHEN 'green' THEN 'go' END;
????SELECT CASE 9 WHEN 1 THEN 'a' WHEN 2 THEN 'b' ELSE 'N/A' END;
????SELECT CASE WHEN (2+2)=4 THEN 'OK' WHEN(2+2)<>4 THEN 'not OK' END ASSTATUS;
????SELECT Name??IF((IsActive = 1)??'?????'??'δ????') AS RESULT FROMUserLoginInfo;
????SELECT fname??lname??(math+sci+lit) AS total??
????CASE WHEN (math+sci+lit) < 50 THEN 'D'
????WHEN (math+sci+lit) BETWEEN 50 AND 150 THEN 'C'
????WHEN (math+sci+lit) BETWEEN 151 AND 250 THEN 'B'
????ELSE 'A' END
????AS grade FROM marks;
????SELECT IF(ENCRYPT('sue'??'ts')=upass??'allow'??'deny') AS LoginResultFROM users WHERE uname = 'sue';#?????????
????????????????
????DATE_FORMAT(date??fmt) ?????????fmt?????????date?
????FORMAT(x??y) ??x??????????????????????У?y??????С??λ??
????INET_ATON(ip) ????IP???????????
????INET_NTOA(num) ???????????????IP???
????TIME_FORMAT(time??fmt) ?????????fmt????????time?
???????м?????FORMAT()????????????????????????????????????????С?
?????????
????????????:
????SELECT FORMAT(34234.34323432??3);
????SELECT DATE_FORMAT(NOW()??'%W??%D %M %Y %r');
????SELECT DATE_FORMAT(NOW()??'%Y-%m-%d');
????SELECT DATE_FORMAT(19990330??'%Y-%m-%d');
????SELECT DATE_FORMAT(NOW()??'%h:%i %p');
????SELECT INET_ATON('10.122.89.47');
????SELECT INET_NTOA(175790383);
??????????????????
???????????????????????MySQL????CAST()????????????????????????????????????????У?BINARY??CHAR??DATE??TIME??DATETIME??SIGNED??UNSIGNED
?????????
????????????:
????SELECT CAST(NOW() AS SIGNED INTEGER)??CURDATE()+0;
????SELECT 'f'=BINARY 'F'??'f'=CAST('F' AS BINARY);
????????????????
????DATABASE() ?????????????
????BENCHMARK(count??expr) ??????expr???????count??
????CONNECTION_ID() ???????????????ID
????FOUND_ROWS() ????????SELECT??????м???????????
????USER()??SYSTEM_USER() ??????????????
????VERSION() ????MySQL????????汾
?????????
????????????:
????SELECT DATABASE()??VERSION()??USER();
????SELECTBENCHMARK(9999999??LOG(RAND()*PI()));#?????У?MySQL????LOG(RAND()*PI())????9999999?Ρ?