Oracle與Mysql的字元連線函式concat與||
1、Oracle版本：
1.1、執行語句：SELECT 'k' as a1,'a' as a2 ,'y' as a3 FROM sr_main
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1 k a y
2 k a y
3 k a y
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1.2執行語句：SELECT concat
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1 ka
2 ka
3 ka
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1.3執行語句：SELECT concat( 'k','a','y') as pj FROM sr_main
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Error：invalid number of arguments
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Reason：Concat只能連線兩個字串
1.4執行語句：SELECT 'k'||'a'||'y' as pj FROM sr_main
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1 kay
2 kay
3 kay
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2、Mysql版本：
2.1執行語句：SELECT concat( 'k','a') as pj FROM sr_main
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ka
ka
Ka
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2.2執行語句：SELECT concat( 'k','a','y') as pj FROM sr_main
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kay
kay
Kay
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2.3執行語句：SELECT 'k'||'a'||'y' as pj FROM sr_main
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0
0
0
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分析兩者差異：
Oracle中可以用||拼接多個字串，但用concat只能拼兩個，否則報錯
Mysql中可以用concat拼接多個，但用||無法拼接字串，會顯示零
綜合兩者：SELECT concat(concat( 'k','a'),'y') as pj FROM sr_main
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kay
kay
Kay
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此方法可以實現兩者通用