SQL基本语句

一.DDL语句
删除表

DROP TABLE IF EXISTS 't_student';

创建表

CREATE TABLE IF NOT EXISTS 't_student' (
        'id' INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
        'name' TEXT,
        'age' INTEGER
);

二 .DML语句
插入数据

INSERT INTO t_student (name, age) VALUES ('why', 18);
INSERT INTO t_student (name, age) VALUES ('lmj', 25);
INSERT INTO t_student (name, age) VALUES ('lnj', 22);
INSERT INTO t_student (name, age) VALUES ('yz', 17);
INSERT INTO t_student (name, age) VALUES ('wsz', 28);

更新数据

UPDATE t_student SET age = 30 WHERE name = 'why';
UPDATE t_student SET name = 'zs' WHERE age > 20;

删除数据

DELETE FROM t_student WHERE name = 'zs’;

三.DQL语句
1.基本查询

SELECT * FROM t_student; 

2.查询特殊的字段

SELECT name, age FROM t_student; 

3.通过条件来查询语句

SELECT name, age FROM t_student WHERE age <= 25; 

4.通过条件查询(模糊查询)

SELECT name, age FROM t_student WHERE name LIKE '%l%'; 

5.多个条件的查询

SELECT name, age FROM t_student WHERE name LIKE '%l%' AND age >= 25;
SELECT name, age FROM t_student WHERE name LIKE '%l%' OR age >= 25;

6.计算个数

SELECT count(*) FROM t_student; SELECT count(name) FROM t_student; SELECT count(age) FROM t_student;

7.数据的排序
1> 升序 ASC(默认)

SELECT * FROM t_student ORDER BY age;

2> 降序 DESC

SELECT * FROM t_student ORDER BY age DESC;

3> 以年龄的升序排序,如果年龄相同,以名字的降序排序

SELECT * FROM t_student ORDER BY age, name DESC;

8.起别名
1> 给表起别名

SELECT s.name, s.age FROM t_student AS s;

2> 给字段起别名

SELECT name AS myName, age AS myAge FROM t_student;

9.分页查询(limit)
1> 基本分

SELECT name, age FROM t_student LIMIT 4, 2; 

2> 该语句的意思是:跳过0条数据,查询前五条数据

 SELECT name, age FROM t_student LIMIT 5;