MYSQL语句5

1.COUNT函数，DISTINCT是不同值。

%%sql 
SELECT COUNT(DISTINCT Dog_Guid)
FROM complete_tests 
WHERE created_at > '2014-03-01'

2. SUM 函数

%%sql 
SELECT SUM(ISNULL(exclude))
FROM dogs

3. AVG, MIN, MAX函数

%%sql 
SELECT test_name,
AVG(rating) AS "AVG_Rating",
MIN(rating) AS "MIN_Rating",
MAX(rating) AS "MAX_Rating"
FROM reviews 
WHERE test_name="Memory versus Pointing"

4.统计时间差 TIMESTAMPDIFF函数

%%sql
SELECT AVG(TIMESTAMPDIFF(MINUTE, start_time, end_time)) AS "AVG_time"
FROM exam_answers
WHERE test_name = "Treat Warm-Up"

%%sql 
SELECT *
FROM exam_answers
WHERE TIMESTAMPDIFF(MINUTE, start_time, end_time) < 0