SQLite - AVG语句

SELECT AVG(aggregate_expression)
FROM tables
[WHERE conditions]; 

SELECT expression1, expression2, ... expression_n
AVG(aggregate_expression)
FROM tables
[WHERE conditions]
GROUP BY expression1, expression2, ... expression_n; 

SELECT AVG(FEES) AS "Avg Fees"
FROM STUDENT
WHERE ID <= 5; 

SELECT AVG(DISTINCT  FEES) AS "Avg Fees"
FROM STUDENT
WHERE FEES > 10000; 

SELECT AVG(FEES/12) AS "Average Monthly Fees"
FROM STUDENT;

SELECT NAME, SUM(FEES) AS "Avg Fees by Name"
FROM STUDENT
GROUP BY AGE;