SQL：sqlite3数据库常用操作

-- 新增表
CREATE TABLE IF NOT EXISTS "user" (
    "id" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
    "name" TEXT,
    "age" INTEGER,
    "icon" TEXT
);
-- 插入记录
INSERT INTO user (name, age, icon) VALUES ("Tom", 23, "Tom_icon");
INSERT INTO user (name, age, icon) VALUES ("Jimi", 24, "Jimi_icon");
INSERT INTO user (name, age, icon) VALUES ("Jack", 25, "Jack_icon");
INSERT INTO user (name, age, icon) VALUES ("Mike", 26, "Mike_icon");
-- 新建表，从已有表导入记录
CREATE TABLE IF NOT EXISTS new_user(
    id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
    name TEXT
) 
INSERT INTO new_user(name) SELECT name FROM user; 

-- 新建一个临时表
CREATE TABLE IF NOT EXISTS "user_name" ("name" TEXT);
-- 删除表
DROP TABLE IF EXISTS user_name;
-- 删除记录
DELETE FROM user WHERE id = 1;

-- 修改表
ALTER TABLE user RENAME TO new_user;
ALTER TABLE new_user RENAME TO user;
-- 表结尾增加一列
ALTER TABLE "user" ADD COLUMN note TEXT;
-- 修改记录
UPDATE user SET name = "杰克" WHERE name = "Jack";
UPDATE user SET name = "汤姆" WHERE name = "Tom";
UPDATE user SET icon = "iconxxx" WHERE age >= 25;

-- 查询 * 表示所有
SELECT * FROM user;
-- 查询部分字段
SELECT name, age FROM user;
-- 条件约束
SELECT name FROM user WHERE age >= 25;
-- 模糊查询  使用like关键词 %零个或多个
SELECT name, icon FROM user WHERE icon LIKE "%icon%";
-- 模糊查询   "_" 一个字符 
SELECT name FROM user WHERE name LIKE "汤_";
-- 查询数量
SELECT COUNT(*) FROM user;
SELECT COUNT(name) FROM user;
-- 排序  默认：ASC (ascend)  升序
SELECT * FROM user ORDER BY age;
-- 降序 DESC (desend) 
SELECT * FROM user ORDER BY age DESC;
-- 分页查询 LIMIT， 查询5条
SELECT * FROM user LIMIT 5;
-- 前面跳过3条，查询5条
SELECT * FROM user LIMIT 3, 5;
-- 字段别名
SELECT name AS n, age AS a FROM user;
-- 表别名
SELECT t.name, t.age FROM user AS t;