MySQL查詢語言操做

筆記:查詢語言操做DQL

操做數據表tb_train_cpp2爲例:

SELECT * FROM tb_train_cpp2;[查詢所有字段]
SELECT userId,userName,salary FROM tb_train_cpp2;[查詢指定字段]
SELECT userName AS '姓名',age AS '年齡',hobby AS '興趣' FROM tb_train_cpp2;[爲指定字段起別名進行查詢]

SELECT * FROM tb_train_cpp2 WHERE age=28;[WHERE:比較運算符]
SELECT * FROM tb_train_cpp2 WHERE age<25;
SELECT * FROM tb_train_cpp2 WHERE age>30;

SELECT * FROM tb_train_cpp2 WHERE hobby is NULL;[WHERE:NULL/NOT NULL]
SELECT userId,userName,userCard FROM tb_train_cpp2 WHERE hobby IS NOT NULL AND age<20;
SELECT userId,userName,userCard FROM tb_train_cpp2 WHERE hobby IS NOT NULL AND sex='男';

SELECT * FROM tb_train_cpp2 WHERE nationName LIKE '__';[WHERE:LIKE模糊查詢]
SELECT * FROM tb_train_cpp2 WHERE userCard LIKE '1%5';
SELECT * FROM tb_train_cpp2 WHERE userName LIKE '孫%';
注:_:表示匹配單個字符/%:匹配0,1,多個字符

SELECT * FROM tb_train_cpp2 WHERE salary BETWEEN 85 AND 95;
SELECT sex,GROUP_CONCAT(userName),COUNT(*) FROM tb_train_cpp2 WHERE age<30 GROUP BY sex;

SELECT * FROM tb_train_cpp2 ORDER BY salary DESC;[按指定字段順序排列:ASC升序/DESC降序]
SELECT * FROM tb_train_cpp2 ORDER BY age ASC;

SELECT * FROM tb_train_cpp2 WHERE userName IN('曹操','甄姬');
SELECT * FROM tb_train_cpp2 WHERE userName LIKE '__' AND nationName IN('中國','英國','美國');

ALTER TABLE tb_train_cpp2 ADD country CHAR(5) AFTER sex;[添加字段country]
UPDATE tb_train_cpp2 SET country='蜀國' WHERE userName IN('關羽','張飛','黃月英','劉備','趙子龍');
UPDATE tb_train_cpp2 SET country='魏國' WHERE userName IN('曹操','甄姬');
UPDATE tb_train_cpp2 SET country='吳國' WHERE userName IN('孫尚香','太史慈','孫權');

SELECT country,GROUP_CONCAT(userName),COUNT(*) FROM tb_train_cpp2 GROUP BY country;
SELECT sex,GROUP_CONCAT(userName),GROUP_CONCAT(userCard),COUNT(*) FROM tb_train_cpp2 GROUP BY sex;
SELECT sex,GROUP_CONCAT(userName),AVG(age) FROM tb_train_cpp2 WHERE country IN('魏國','蜀國') GROUP BY sex;
SELECT country,GROUP_CONCAT(userName),
COUNT(*) AS '組中人數',
MAX(age) AS '最大年齡',
MIN(salary) AS '最小能力值'
FROM tb_train_cpp2 WHERE age<30 AND userName LIKE '__'
GROUP BY country;

SELECT age,GROUP_CONCAT(userName),COUNT(*) FROM tb_train_cpp2[HAVING字句只能接分組查詢]
WHERE salary BETWEEN 85 AND 95 GROUP BY age
HAVING COUNT(*)>1;

SELECT * FROM tb_train_cpp2 WHERE country IN('吳國','魏國') AND userName LIKE '__'
ORDER BY age LIMIT 1;

建立數據表tb_train_cpp22[之後作外鍵操做]CREATE TABLE IF NOT EXISTS tb_train_cpp22(cid INT UNSIGNED KEY AUTO_INCREMENT,cname CHAR(5) NOT NULL UNIQUE, people_num INT UNSIGNED)ENGINE=INNODB CHARSET=UTF8;INSERT tb_train_cpp22(cname,people_num) VALUES('魏國',1500),('吳國',1250),('蜀國',980);