- null key (characteristic)英語什么意思：A flag associated with an alternate key that indicates whether or not a null key value is defined for the key. For binary, integer, and packed decimal key data types, the null key value is zero expressed in that data type. For the string key data type, users must specify a byte value from 000(8) through 377(8) including ASCII codes.; 和某個替換關(guān)鍵字相聯(lián)系的標(biāo)志，用于指示是否為該關(guān)鍵字定義了一個空關(guān) 鍵字值。對于二進(jìn)制數(shù)、整數(shù)和壓縮十進(jìn)制關(guān)鍵字?jǐn)?shù)據(jù)類型，空關(guān)鍵字值為零，并表示為該 數(shù)據(jù)類型的形式。對于字符串關(guān)鍵字?jǐn)?shù)據(jù)類型，用戶必須指定一個字節(jié)的數(shù)值，從八進(jìn)制的 000到377，其中包括了ASCII字符的代碼。
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