SQL: select round(788.6) from dual; //不指定时，默认小数点后第一位开始四舍五入
RESULT: 789
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SQL: select round(788.6,-1) from dual; //指定整数位开始四舍五入
RESULT: 790
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SQL: select round(788.446, 2) from dual; //指定保留的小数位数，四舍五入
RESULT: 788.45
SQL: select round(788.441, 2) from dual; //指定保留的小数位数，四舍五入
RESULT: 788.44
