數據分析挖掘之——sql複習

select name from people where name  like '_r%' # 第二個字母是r，前面有幾個_就說明是n+1位是r

select avg(gross) from films # 此代碼只會平均gross不爲空的數據，爲空的不計
下列兩行代碼結果一致

select (4/3) # 向下取整，結果是1
select (4.0/3.0) # 浮點數

select release_year,avg(budget) as avg_budget,avg(gross) avg_gross from films 
where release_year > 1990 group by release_year having avg(budget) > 60000000
order by avg_gross desc
---注意having的使用