1.字符函数
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全部小写
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全部大写
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首字母大写
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'要截取的字符串',起始位置说明：位置从1开始
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--instr('大字符串','小字符串')返回小字符串在大字符串中出现的位置
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2.日期函数
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3.转换函数
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4.数字函数
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5.通用函数
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6.decode函数
