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1. nvl :é对空å¼è¿è¡æµè¯
å½æ°åå为ï¼NVL(testValue,SubstituteValue)
常è§çç¨æ³æ¯ Select max(score) From SC Where Name=âJerryâ
ææ¶max(score)为空ï¼ä¹å°±æ¯è¯´Jerry并没æèè¯è®°å½ï¼è¿æ¶æ们ç¨"No Record"æ 注ä¸ä¸ï¼
Select NVL(max(score),"No Record") From SC;
è¿æä¸ä¸ªNVL2å½æ°è·å ¶ç¸ä¼¼ï¼å½æ°ååä¸ºï¼ NVL(testValue,SubValue1ï¼SubValue2)
NVL2å½æ°å®ç°çæ¯è¥testValue为NULLï¼è¿åSubValue1ï¼å¦åè¿åSubValue2ã
2.Decodeå½æ°
Decodeå½æ°çåå为: Decode(testValue, if1, then1, if2,then2.....else).
é对testValueè¿è¡æµè¯ï¼è¥testValueçäºif1åè¿åthen1,è¥testValueçäºif2åè¿åthen2,....è¥é½æ²¡æè¿åï¼åè¿åelse. 示ä¾å¦ä¸ï¼
è¥æ们ç¨Decodeå¯ä»¥è¿æ ·å®ç°ï¼
SELECT class, course,
DECODE (student,
'A', 'Anco',
'B', 'Bily',
'C', 'Candy',
'D', 'Davi',
'E', 'Eve',
'F', 'Fion'
) AS en_name
FROM studentinfo
3. to_charå½æ°åè½ï¼å°±æ¯å°æ°å¼åæè æ¥æå转å为å符åï¼è½¬æ¢è¿ç¨ä¸å¯ä»¥è¿è¡æ ¼å¼åå¤çï¼å½æ°ååè¾å¤ï¼ç¤ºä¾å¦ä¸ï¼