NULL 谓词
NULL 谓词测试是否是 null 值。
使用语法:
single-valued-path-expression IS [NOT] NULL
示例:NULL 谓词
e.name IS NULL
e.dept.name IS NOT NULL
e.dept IS NOT NULL
NULL 谓词测试是否是 null 值。
single-valued-path-expression IS [NOT] NULL
e.name IS NULL
e.dept.name IS NOT NULL
e.dept IS NOT NULL