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chu xue zhe bi du : ti gao SQL zhi xing xiao lv de ji dian jian yi

2008-08-08 06:10:15 编辑來源:互联网 评论
 
本文为【初学者必读:提高SQL执行效率的几点建议】的拼音翻译版
  ti gao SQL zhi xing xiao lv de ji dian jian yi :
  ◆ jin liang bu yao zai where zhong bao han zi cha xun ;
  guan yu shi jian de cha xun , jin liang bu yao xie cheng :where to_char(dif_date,'yyyy-mm-dd')=to_char('2007-07-01','yyyy-mm-dd');
  ◆ zai guo lv tiao jian zhong , ke yi guo lv diao zui da shu liang ji lu de tiao jian bi xu fang zai where zi ju de mo yi ;
  FROM zi ju zhong xie zai zui hou de biao ( ji chu biao ,driving table) jiang bei zui xian chu li , zai FROM zi ju zhong bao han duo ge biao de qing kuang xia , ni bi xu xuan ze ji lu tiao shu zui shao de biao zuo wei ji chu biao 。 ru guo you san ge yi shang de lian jie cha xun , na jiu xu yao xuan ze jiao cha biao (intersection table) zuo wei ji chu biao , jiao cha biao shi zhi na ge bei qi ta biao suo yin yong de biao ;
  ◆ cai yong bang ding bian liang
  ◆ zai WHERE zhong jin liang bu yao shi yong OR
  ◆ yong EXISTS ti dai IN、 yong NOT EXISTS ti dai NOT IN;
  ◆ bi mian zai suo yin lie shang shi yong ji suan :WHERE SAL*12>25000;
  ◆ yong IN lai ti dai OR: WHERE LOC_ID=10 OR LOC_ID=15 OR LOC_ID=20
  ◆ bi mian zai suo yin lie shang shi yong IS NULL he IS NOT NULL;
  ◆ zong shi shi yong suo yin de di yi ge lie ;
  ◆ yong UNION-ALL ti dai UNION;
  ◆ bi mian gai bian suo yin lie de lei xing :SELECT...FROM EMP WHERE EMPNO='123', you yu yin shi shu ju lei xing zhuan huan ,to_char(EMPNO)='123', yin ci , jiang bu cai yong suo yin , yi ban zai cai yong zi fu chuan pin cou dong tai SQL yu ju chu xian ;
  ◆'!=' jiang bu shi yong suo yin ;
  ◆ you hua GROUP BY;
  ◆ bi mian dai you LIKE shen shu de tong pei fu ,LIKE '4YE%' shi yong suo yin , dan LIKE '%YE' bu shi yong suo yin
  ◆ bi mian shi yong kun nan de zheng gui biao da shi , li ru select * from customer where zipcode like "98___", ji bian zai zipcode shang jian li le suo yin , zai zhe zhong qing kuang xia ye huan shi cai yong shun xu sao miao de fang shi 。 ru guo ba yu ju gai cheng select * from customer where zipcode>"98000", zai zhi xing cha xun shi jiu hui li yong suo yin lai cha xun , xian ran hui da da ti gao su du ;
  ◆ jin liang ming que de wan cheng SQL yu ju , jin liang shao rang shu ju ku gong zuo 。 bi ru xie SELECT yu ju shi , xu yao ba cha xun de zi duan ming que zhi chu biao ming 。 jin liang bu yao shi yong SELECT * yu ju 。 zu zhi SQL yu ju de shi hou , jin liang an zhao shu ju ku de xi guan jin xing zu zhi 。【原文】【汉音对照
 
 
 
 
 
 
 
 
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ti gao SQL zhi xing xiao lv de ji dian jian yi : ◆ jin liang bu yao zai where zhong bao han zi cha xun ; guan yu shi jian de cha xun , jin liang bu yao xie cheng :where to_char(dif_date,'yyyy-mm-dd')=to_char('2007-07-01','yyyy-mm-dd'); ◆ zai guo lv tiao jian zhong , ke yi guo lv diao zui da shu liang ji lu de tiao jian bi xu fang zai where zi ju de mo yi ; FROM zi ju zhong xie zai zui hou de biao ( ji chu biao ,driving table) jiang bei zui xian chu li , zai FROM zi ju zhong bao han duo ge biao de qing kuang xia , ni bi xu xuan ze ji lu tiao shu zui shao de biao zuo wei ji chu biao 。 ru guo you san ge yi shang de lian jie cha xun , na jiu xu yao xuan ze jiao cha biao (intersection table) zuo wei ji chu biao , jiao cha biao shi zhi na ge bei qi ta biao suo yin yong de biao ; ◆ cai yong bang ding bian liang ◆ zai WHERE zhong jin liang bu yao shi yong OR ◆ yong EXISTS ti dai IN、 yong NOT EXISTS ti dai NOT IN; ◆ bi mian zai suo yin lie shang shi yong ji suan :WHERE SAL*12>25000; ◆ yong IN lai ti dai OR: WHERE LOC_ID=10 OR LOC_ID=15 OR LOC_ID=20 ◆ bi mian zai suo yin lie shang shi yong IS NULL he IS NOT NULL; ◆ zong shi shi yong suo yin de di yi ge lie ; ◆ yong UNION-ALL ti dai UNION; ◆ bi mian gai bian suo yin lie de lei xing :SELECT...FROM EMP WHERE EMPNO='123', you yu yin shi shu ju lei xing zhuan huan ,to_char(EMPNO)='123', yin ci , jiang bu cai yong suo yin , yi ban zai cai yong zi fu chuan pin cou dong tai SQL yu ju chu xian ; ◆'!=' jiang bu shi yong suo yin ; ◆ you hua GROUP BY; ◆ bi mian dai you LIKE shen shu de tong pei fu ,LIKE '4YE%' shi yong suo yin , dan LIKE '%YE' bu shi yong suo yin ◆ bi mian shi yong kun nan de zheng gui biao da shi , li ru select * from customer where zipcode like "98___", ji bian zai zipcode shang jian li le suo yin , zai zhe zhong qing kuang xia ye huan shi cai yong shun xu sao miao de fang shi 。 ru guo ba yu ju gai cheng select * from customer where zipcode>"98000", zai zhi xing cha xun shi jiu hui li yong suo yin lai cha xun , xian ran hui da da ti gao su du ; ◆ jin liang ming que de wan cheng SQL yu ju , jin liang shao rang shu ju ku gong zuo 。 bi ru xie SELECT yu ju shi , xu yao ba cha xun de zi duan ming que zhi chu biao ming 。 jin liang bu yao shi yong SELECT * yu ju 。 zu zhi SQL yu ju de shi hou , jin liang an zhao shu ju ku de xi guan jin xing zu zhi 。
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