具体使用
UPDATE t_student SET name = 'me' WHERE age = 14; UPDATE t_student SET name = 'liu' WHERE age is 20; UPDATE t_student SET name = 'yy' WHERE age < 20; UPDATE t_student SET name = 'A' WHERE age < 100 and score > 60; UPDATE t_student SET name = 'ly';
删除数据
DELETE FROM t_student; DELETE FROM t_student WHERE age < 30;
语法说明
DELETE FROM: 从表中删除数据
t_student : 表名
可以跟条件也可以不跟:不跟表示删除所有的数据
DQL语句
查询语句
基本查询(查询整个表格)
SELECT * FROM t_student;
查询某些字段(查询name和age两个字段)
SELECT name, age FROM t_student;
通过条件判断来查询对应的数据(年龄大于等于18)
SELECT * FROM t_student WHERE age >= 18;
通过条件判断来查询对应的数据(名字以i开头),使用like关键字(模糊查询)
SELECT * FROM t_student WHERE name like '%i%';
计算个数
计算一共多少列
SELECT count(*) FROM t_student;
计算某一个列个数
SELECT count(age) FROM t_student;
排序
升序 ASC (默认是升序)
SELECT * FROM t_student ORDER BY age;
降序 DESC
SELECT * FROM t_student ORDER BY age DESC;
按照年龄升序排序,如果年龄相同,按照名字的降序排列
SELECT * FROM t_student ORDER BY age,name DESC;
起别名
给列起别名(as可以省略)
SELECT name AS myName, age AS myAge FROM t_student;
给表起别名
SELECT s.name, s.age FROM t_student as s;
limit
SELECT * FROM t_student LIMIT 数字1,数字2;
跳过前9条数据,再查询3条数据
SELECT * FROM t_student LIMIT 9, 3;