????· ???? ??
????????????????????????????????
????WHERE p.name <=> NULL
????????????????? <=>????????????????????? =?????????????????????????????????????魏未????????????????????mysql?械? <> = !=??????

????· ???? ??
??????=????????
?????????=??????????????????斜????????0???????????1??????;???浠�???’A'<=>’B'??0??’a'<=>’a‘??1??
????2.??=???????
??????=?????????????NULL?????????魏???????????=????????????NULL?????效????????????????<=>??
????'a' <=> NULL ??0   NULL<=> NULL ?贸? 1????=???????????=????????????? 'a'=NULL ?????NULL ????NULL = NULL ??????NULL?????????mysql????????械???????????????????????????????NULL???????????????濉�

????· ???
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????... WHERE col_a <=> ? ...
??????????位???锌??????????锌?????NULL???????<=>????????????斜????????????魏?????

????· ????????
???????? <=> ???????????????????????????????????NULL?????????IS NULL and IS NOT NULL????????ANSI????械?????????????????????????????小???<=>?????mysql????谩?
??????????<=>????mysql?械?????
????'a' IS NULL     ==> 'a' <=> NULL
????'a' IS NOT NULL ==> NOT('a' <=> NULL)
???????????????????????胃?????????????
????WHERE p.name IS NULL