Oracle之NULL IS NULL
Oracle之NULL IS NULL
NULL 不 大于/小于/等于/不等于 任何值(包括NULL本身),有且仅有:NULL IS NULL
- SQL> set serveroutput on
- SQL>
- SQL> BEGIN
- 2 IF (2 > NULL)
- 3 THEN
- 4 dbms_output.put_line('>');
- 5 ELSIF (2 < NULL)
- 6 THEN
- 7 dbms_output.put_line('<');
- 8 ELSIF (2 = NULL)
- 9 THEN
- 10 dbms_output.put_line('=');
- 11 ELSIF (2 != NULL)
- 12 THEN
- 13 dbms_output.put_line('!=');
- 14 ELSE
- 15 dbms_output.put_line('Unknown!');
- 16 END IF;
- 17
- 18 IF (NULL = NULL)
- 19 THEN
- 20 dbms_output.put_line('NULL = NULL');
- 21 ELSIF (NULL != NULL)
- 22 THEN
- 23 dbms_output.put_line('NULL != NULL');
- 24 ELSIF (NULL IS NULL)
- 25 THEN
- 26 dbms_output.put_line('NULL IS NULL');
- 27 ELSE
- 28 dbms_output.put_line('UNKNOWN!!');
- 29 END IF;
- 30 END;
- 31 /
- Unknown!
- NULL IS NULL
- PL/SQL procedure successfully completed
- SQL>
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