oracle11g - Oracle SQL join three tables and group by column -

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i have 3 tables , want query te select teacher names , number of classes each teacher has reserved.

teacher:

| idt | name |

class:

| idc | name |

reserve:

| idc | idt |

my query:

select   t.name, count(distinct(r.idc))     teacher t   join    reserve r   on   r.idt = t.idt   join   class c   on   c.idc = r.idc   group r.idc

when run followin error: not group expression.

the group by clause needs contain non-aggregated columns select statement; in case should t.name. also, distinct not function keyword , should not have parentheses.

select   t.name,    count(distinct r.idc) number_of_classes   teacher t join    reserve r on r.idt = t.idt join   class c on c.idc = r.idc group    t.name

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