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3. case when  ±í´ïʽ then ''
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             else    ''
   end
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5.null ÒªÏëÅжÏÖµÊÇ·ñΪnull±ØÐëΪ is null  £¬ null²»ÄÜÓõÈÓÚ=ºÍ²»µÈÓÚ<> ºÍÈκÎÖµ±È½Ï°üÀ¨null
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sqlµ÷ÓÅÖ® ѰÕÒÎÒÃÇ×î¸ÐÐËȤµÄÓï¾ä

Tuning an Application / Reducing Load
If your whole application is performing suboptimally, or if you are attempting to
reduce the overall CPU or I/O load on the database server, then identifying
resource-intensive SQL involves the following steps:
1. Determine which period in the day you would ......
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