mysql 語句

數據庫：
SQL
四大操做語句-
1.刪 DELETE
DELETE FROM 表 WHERE 條件

2.增 INSERT
INSERT INTO 表 (字段列表) VALUES(值列表)

3.改 UPDATE
UPDATE 表 SET 字段=值,字段=值,... WHERE 條件

4.查 SELECT
SELECT * FROM 表 WHERE 條件

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子句：
WHERE 條件

WHERE name='blue'
WHERE age>18
WHERE age<=18
WHERE age>=18 AND score<60
WHERE cach>100 OR score>10000

ORDER 排序
ORDER BY age ASC/DESC
ASC-升序(從小到大)
DESC-降序(從大到小)

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ORDER BY price ASC

*價格(price)升序排序，若是價格相同，再按銷量(sales)降序排序
ORDER BY price ASC, sales DESC

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GROUP 聚類-合併相同

*統計每一個班人數
ID class name
"1" "1" "小明"
"2" "2" "小紅"
"3" "1" "小剛"
"4" "2" "小華"
"5" "3" "小強"
"6" "3" "小四"
"7" "1" "小劉"
"8" "1" "小花"

SELECT * FROM student_table;
ID class name
"1" "1" "小明"
"2" "2" "小紅"
"3" "1" "小剛"
"4" "2" "小華"
"5" "3" "小強"
"6" "3" "小四"
"7" "1" "小劉"
"8" "1" "小花"

SELECT * FROM student_table GROUP BY class;
ID class name
"1" "1" "小明"
"2" "2" "小紅"
"5" "3" "小強"

SELECT class FROM student_table GROUP BY class;
class
"1"
"2"
"3"

SELECT class,COUNT(class) FROM student_table GROUP BY class;
class COUNT(class)
1 4
2 2
3 2

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WHERE子句
ORDER子句——多條件排序
GROUP子句——合併
COUNT、MIN、MAX、AVG

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GROUP