A 琛?鏄?浼佷笟鐢ㄦ埛鐨勫熀鏈俊鎭?
SID NAME
--------------
2 AAAA
5 BB
--------------
B 琛?鏄笂闈?A 琛ㄩ噷鐨勪紒涓氫氦鐨勬暟鎹?濡備笅:
SID DATETIME NOTES
------------------------------
2 1998-3-4 XXXX
5 2003-1-3 BBBB
2 2005-8-9 CCCC
2 2005-7-3 CCCC
------------------------------
璇烽棶:
1 : 鎴戣鎵懼嚭 A 琛ㄩ噷, 2005騫?鏈堟湭浜ゆ暟鎹殑浼佷笟搴斿浣曟壘?
2 : 鎴戣鎵?BB 榪欎釜浼佷笟鏈鍚庨掍氦鐨勬暟鎹張濡備綍?
Select * from tbB where SID=a.SID and Datediff(month,DATETIME,'2005-07-01')=0)
SELECT b.*
FROM TABLE1 a INNER JOIN
TABLE2 b ON a.SID = b.SID
WHERE (a.NAME = 'BB') AND (NOT EXISTS
(SELECT *
FROM TABLE2
WHERE SID = b.SID AND DATETIME > b.DATETIME))
]]>
瀛楁鏈?br>1:搴忓彿
2:鍏ュ簱鏃ユ湡
3:鐘舵?br>4:鍑鴻揣鏃ユ湡
鎴戠幇鍦ㄦ兂鍦ㄧ4涓瓧孌佃繘琛屽垽鏂?褰?鐘舵?瀛楁鐨勫間負'out'鐨勬椂鍊?鍑鴻揣鏃ユ湡涓篻etdate
鍚﹀垯鍑鴻揣鏃ユ湡涓虹┖
]]>
id | name
---------
1 | libk
2 | zyfon
3 | daodao
---------
1 | libk
2 | zyfon
3 | daodao
user_action琛?/em>:
user_id | action
---------------
1 | jump
1 | kick
1 | jump
2 | run
4 | swim
---------------
1 | jump
1 | kick
1 | jump
2 | run
4 | swim
sql:
select id, name, action from user as u
left join user_action a on u.id = a.user_id
result:
id | name | action
--------------------------------
1 | libk | jump 鈶?br> 1 | libk | kick 鈶?br> 1 | libk | jump 鈶?br> 2 | zyfon | run 鈶?br> 3 | daodao | null 鈶?/p>
鍒嗘瀽錛?/h5>
娉ㄦ剰鍒皍ser_action涓繕鏈変竴涓猽ser_id=4, action=swim鐨勭邯褰曪紝浣嗘槸娌℃湁鍦ㄧ粨鏋滀腑鍑虹幇錛?br>鑰寀ser琛ㄤ腑鐨刬d=3, name=daodao鐨勭敤鎴峰湪user_action涓病鏈夌浉搴旂殑綰綍錛屼絾鏄嵈鍑虹幇鍦ㄤ簡緇撴灉闆嗕腑
鍥犱負鐜板湪鏄痩eft join錛屾墍鏈夌殑宸ヤ綔浠eft涓哄噯.
緇撴灉1錛?錛?錛?閮芥槸鏃㈠湪宸﹁〃鍙堝湪鍙寵〃鐨勭邯褰曪紝5鏄彧鍦ㄥ乏琛紝涓嶅湪鍙寵〃鐨勭邯褰?br>
緇撹錛?/h5>
鎴戜滑鍙互鎯寵薄left join 鏄繖鏍峰伐浣滅殑
浠庡乏琛ㄨ鍑轟竴鏉★紝閫夊嚭鎵鏈変笌on鍖歸厤鐨勫彸琛ㄧ邯褰?n鏉?榪涜榪炴帴錛?褰㈡垚n鏉＄邯褰?鍖呮嫭閲嶅鐨勮錛屽錛氱粨鏋?鍜岀粨鏋?)錛?br>濡傛灉鍙寵竟娌℃湁涓巓n鏉′歡鍖歸厤鐨勮〃錛岄偅榪炴帴鐨勫瓧孌甸兘鏄痭ull.
鐒跺悗緇х畫璇諱笅涓鏉°?br>
寮曠敵錛?/h5>
鎴戜滑鍙互鐢ㄥ彸琛ㄦ病鏈塷n鍖歸厤鍒欐樉紺簄ull鐨勮寰? 鏉ユ壘鍑烘墍鏈夊湪宸﹁〃錛屼笉鍦ㄥ彸琛ㄧ殑綰綍錛?娉ㄦ剰鐢ㄦ潵鍒ゆ柇鐨勯偅鍒楀繀欏誨０鏄庝負not null鐨勩?br>濡傦細
sql:
select id, name, action from user as u
left join user_action a on u.id = a.user_id
where a.user_id is NULL
(娉ㄦ剰:1.鍒楀間負null搴旇鐢╥s null 鑰屼笉鑳界敤=NULL
2.榪欓噷a.user_id 鍒楀繀欏誨０鏄庝負 NOT NULL 鐨?/strong>)
result:
id | name | action
--------------------------
3 | daodao | NULL
]]>
浠庡乏琛ㄨ鍑轟竴鏉★紝閫夊嚭鎵鏈変笌on鍖歸厤鐨勫彸琛ㄧ邯褰?n鏉?榪涜榪炴帴錛?褰㈡垚n鏉＄邯褰?鍖呮嫭閲嶅鐨勮錛屽錛氱粨鏋?鍜岀粨鏋?)錛?br>濡傛灉鍙寵竟娌℃湁涓巓n鏉′歡鍖歸厤鐨勮〃錛岄偅榪炴帴鐨勫瓧孌甸兘鏄痭ull.
鐒跺悗緇х畫璇諱笅涓鏉°?br>
寮曠敵錛?/h5>
鎴戜滑鍙互鐢ㄥ彸琛ㄦ病鏈塷n鍖歸厤鍒欐樉紺簄ull鐨勮寰? 鏉ユ壘鍑烘墍鏈夊湪宸﹁〃錛屼笉鍦ㄥ彸琛ㄧ殑綰綍錛?娉ㄦ剰鐢ㄦ潵鍒ゆ柇鐨勯偅鍒楀繀欏誨０鏄庝負not null鐨勩?br>濡傦細
sql:
select id, name, action from user as u
left join user_action a on u.id = a.user_id
where a.user_id is NULL
(娉ㄦ剰:1.鍒楀間負null搴旇鐢╥s null 鑰屼笉鑳界敤=NULL
2.榪欓噷a.user_id 鍒楀繀欏誨０鏄庝負 NOT NULL 鐨?/strong>)
result:
id | name | action
--------------------------
3 | daodao | NULL
璇硶
NVL(eExpression1, eExpression2)
鍙傛暟
eExpression1, eExpression2
濡傛灉 eExpression1 鐨勮綆楃粨鏋滀負 null 鍊鹼紝鍒?NVL( ) 榪斿洖 eExpression2銆傚鏋?eExpression1 鐨勮綆楃粨鏋滀笉鏄?null 鍊鹼紝鍒欒繑鍥?eExpression1銆俥Expression1 鍜?eExpression2 鍙互鏄換鎰忎竴縐嶆暟鎹被鍨嬨傚鏋?eExpression1 涓?eExpression2 鐨勭粨鏋滅殕涓?null 鍊鹼紝鍒?NVL( ) 榪斿洖 .NULL.銆?br />
2.decode(鏉′歡,鍊?,緲昏瘧鍊?,鍊?,緲昏瘧鍊?,...鍊糿,緲昏瘧鍊糿,緙虹渷鍊?
聽聽聽 璇ュ嚱鏁扮殑鍚箟濡備笅錛?br />
IF 鏉′歡=鍊? THEN
銆銆銆銆RETURN(緲昏瘧鍊?)
ELSIF 鏉′歡=鍊? THEN
銆銆銆銆RETURN(緲昏瘧鍊?)
銆銆銆銆......
ELSIF 鏉′歡=鍊糿 THEN
銆銆銆銆RETURN(緲昏瘧鍊糿)
ELSE
銆銆銆銆RETURN(緙虹渷鍊?
END IF
聽聽聽 浣跨敤鏂規硶錛毬?br />
聽聽聽 1銆佹瘮杈冨ぇ灝?br />
select decode(sign(鍙橀噺1-鍙橀噺2),-1,鍙橀噺1,鍙橀噺2) from dual; --鍙栬緝灝忓?br />sign()鍑芥暟鏍規嵁鏌愪釜鍊兼槸0銆佹鏁拌繕鏄礋鏁幫紝鍒嗗埆榪斿洖0銆?銆?1
聽聽聽 渚嬪錛?br />
鍙橀噺1=10錛屽彉閲?=20
鍒檚ign(鍙橀噺1-鍙橀噺2)榪斿洖-1錛?u>decode瑙ｇ爜緇撴灉涓衡滃彉閲?鈥濓紝杈懼埌浜嗗彇杈冨皬鍊肩殑鐩殑銆?img src ="http://m.tkk7.com/daipan/aggbug/106376.html" width = "1" height = "1" />
]]>