您不必按选择的完全相同的内容进行分组，例如：
sql:select priority,count(*) from rule_class
group by priority
PRIORITY COUNT(*)
70 1
50 4
30 1
90 2
10 4
sql:select decode(priority,50,'Norm','Odd'),count(*) from rule_class
group by priority
DECO COUNT(*)
Odd 1
Norm 4
Odd 1
Odd 2
Odd 4
sql:select decode(priority,50,'Norm','Odd'),count(*) from rule_class
group by decode(priority,50,'Norm','Odd')
DECO COUNT(*)
Norm 4
Odd 8
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