SQLite 入门教程（四）增删改查，有讲究
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增删改查操作，其中增删改操作被称为数据操作语言 DML，相对来说简单一点。 查操作相对来说复杂一点，涉及到很多子句，所以这篇先讲增删改操作，以例子为主，后面再讲查操作。 |
一、插入数据 INSERT INTO 表（列...） VALUES（值...）
根据前面几篇的内容，我们可以很轻送的创建一个数据表，并向其中插入一些数据，不多说，看例子：
myqiao@ubuntu:~/My Documents/db$ sqlite3 test.db -- Loading resources from /home/myqiao/.sqliterc SQLite version 3.7.4 Enter ".help" for instructions Enter SQL statements terminated with a ";" sqlite> .tables sqlite> sqlite> CREATE TABLE Teachers( ...> Id integer PRIMARY KEY, ...> Name text NOT NULL, ...> Age integer CHECK(Age>22), ...> Country text DEFAULT 'USA'); sqlite> .tables Teachers sqlite> sqlite> INSERT INTO Teachers VALUES(1,'Alice',25,'CHN'); sqlite> INSERT INTO Teachers VALUES(2,'Bob',25,'BRA'); sqlite> INSERT INTO Teachers(Id,Name,Age,Country) VALUES(3,'Charls',33,'USA'); sqlite> INSERT INTO Teachers(Name,Age) VALUES('Jhon',43); sqlite> SELECT * FROM Teachers; Id Name Age Country ---- --------------- --------------- --------------- 1 Alice 25 CHN 2 Bob 25 BRA 3 Charls 33 USA 4 Jhon 43 USA sqlite>
很简单，创建了一个 Teachers 表并向其中添加了四条数据，设定了一些约束，其中有自动增加的主键、默认值等等。
二、修改数据 UPDATE 表 SET 列 = '新值' 【WHERE 条件语句】
UPDATE 语句用来更新表中的某个列，如果不设定条件，则所有记录的这一列都被更新； 如果设定了条件，则符合条件的记录的这一列被更新， WHERE 子句被用来设定条件，如下例：
sqlite> sqlite> SELECT * FROM Teachers; Id Name Age Country ---- --------------- --------------- --------------- 1 Alice 25 CHN 2 Bob 25 BRA 3 Charls 33 USA 4 Jhon 43 USA sqlite> sqlite> sqlite> UPDATE Teachers SET Country='China'; sqlite> SELECT * FROM Teachers; Id Name Age Country ---- --------------- --------------- --------------- 1 Alice 25 China 2 Bob 25 China 3 Charls 33 China 4 Jhon 43 China sqlite> sqlite> sqlite> UPDATE Teachers SET Country='America' WHERE Id=3; sqlite> SELECT * FROM Teachers; Id Name Age Country ---- --------------- --------------- --------------- 1 Alice 25 China 2 Bob 25 China 3 Charls 33 America 4 Jhon 43 China sqlite> sqlite> sqlite> UPDATE Teachers SET Country='India' WHERE Age<30; sqlite> SELECT * FROM Teachers; Id Name Age Country ---- --------------- --------------- --------------- 1 Alice 25 India 2 Bob 25 India 3 Charls 33 America 4 Jhon 43 China sqlite>
三、删除数据 DELETE FROM 表 【WHERE 条件语句】
如果设定 WHERE 条件子句，则删除符合条件的数据记录；如果没有设定条件语句，则删除所有记录
sqlite> sqlite> SELECT * FROM Teachers; Id Name Age Country ---- --------------- --------------- --------------- 1 Alice 25 India 2 Bob 25 India 3 Charls 33 America 4 Jhon 43 China sqlite> sqlite> sqlite> DELETE FROM Teachers WHERE Age>30; sqlite> SELECT * FROM Teachers; Id Name Age Country ---- --------------- --------------- --------------- 1 Alice 25 India 2 Bob 25 India sqlite> sqlite> sqlite> DELETE FROM Teachers; sqlite> SELECT * FROM Teachers; sqlite>
四、查找数据 SELECT 列... FROM 表
为了后面的练习，需要一些样本数据。 首先将下面的 SQL 语句保存到 data.sql 文件中
BEGIN TRANSACTION;
CREATE TABLE Cars(Id integer PRIMARY KEY, Name text, Cost integer);
INSERT INTO Cars VALUES(1,'Audi',52642);
INSERT INTO Cars VALUES(2,'Mercedes',57127);
INSERT INTO Cars VALUES(3,'Skoda',9000);
INSERT INTO Cars VALUES(4,'Volvo',29000);
INSERT INTO Cars VALUES(5,'Bentley',350000);
INSERT INTO Cars VALUES(6,'Citroen',21000);
INSERT INTO Cars VALUES(7,'Hummer',41400);
INSERT INTO Cars VALUES(8,'Volkswagen',21600);
COMMIT;
BEGIN TRANSACTION;
CREATE TABLE Orders(Id integer PRIMARY KEY, OrderPrice integer CHECK(OrderPrice>0),
Customer text);
INSERT INTO Orders(OrderPrice, Customer) VALUES(1200, "Williamson");
INSERT INTO Orders(OrderPrice, Customer) VALUES(200, "Robertson");
INSERT INTO Orders(OrderPrice, Customer) VALUES(40, "Robertson");
INSERT INTO Orders(OrderPrice, Customer) VALUES(1640, "Smith");
INSERT INTO Orders(OrderPrice, Customer) VALUES(100, "Robertson");
INSERT INTO Orders(OrderPrice, Customer) VALUES(50, "Williamson");
INSERT INTO Orders(OrderPrice, Customer) VALUES(150, "Smith");
INSERT INTO Orders(OrderPrice, Customer) VALUES(250, "Smith");
INSERT INTO Orders(OrderPrice, Customer) VALUES(840, "Brown");
INSERT INTO Orders(OrderPrice, Customer) VALUES(440, "Black");
INSERT INTO Orders(OrderPrice, Customer) VALUES(20, "Brown");
COMMIT;
CREATE TABLE Cars(Id integer PRIMARY KEY, Name text, Cost integer);
INSERT INTO Cars VALUES(1,'Audi',52642);
INSERT INTO Cars VALUES(2,'Mercedes',57127);
INSERT INTO Cars VALUES(3,'Skoda',9000);
INSERT INTO Cars VALUES(4,'Volvo',29000);
INSERT INTO Cars VALUES(5,'Bentley',350000);
INSERT INTO Cars VALUES(6,'Citroen',21000);
INSERT INTO Cars VALUES(7,'Hummer',41400);
INSERT INTO Cars VALUES(8,'Volkswagen',21600);
COMMIT;
BEGIN TRANSACTION;
CREATE TABLE Orders(Id integer PRIMARY KEY, OrderPrice integer CHECK(OrderPrice>0),
Customer text);
INSERT INTO Orders(OrderPrice, Customer) VALUES(1200, "Williamson");
INSERT INTO Orders(OrderPrice, Customer) VALUES(200, "Robertson");
INSERT INTO Orders(OrderPrice, Customer) VALUES(40, "Robertson");
INSERT INTO Orders(OrderPrice, Customer) VALUES(1640, "Smith");
INSERT INTO Orders(OrderPrice, Customer) VALUES(100, "Robertson");
INSERT INTO Orders(OrderPrice, Customer) VALUES(50, "Williamson");
INSERT INTO Orders(OrderPrice, Customer) VALUES(150, "Smith");
INSERT INTO Orders(OrderPrice, Customer) VALUES(250, "Smith");
INSERT INTO Orders(OrderPrice, Customer) VALUES(840, "Brown");
INSERT INTO Orders(OrderPrice, Customer) VALUES(440, "Black");
INSERT INTO Orders(OrderPrice, Customer) VALUES(20, "Brown");
COMMIT;
然后在在终端执行命令 .read data.sql，将数据导入到数据库中
sqlite> sqlite> .tables Friends sqlite> .read data.sql sqlite> .tables Cars Orders Teachers sqlite>
可以看到，Cars 表和 Orders 表已经导入到数据库中，现在可以查询了
sqlite> sqlite> SELECT * FROM Cars; Id Name Cost ---- --------------- --------------- 1 Audi 52642 2 Mercedes 57127 3 Skoda 9000 4 Volvo 29000 5 Bentley 350000 6 Citroen 21000 7 Hummer 41400 8 Volkswagen 21600 sqlite> SELECT * FROM Orders; Id OrderPrice Customer ---- --------------- --------------- 1 1200 Williamson 2 200 Robertson 3 40 Robertson 4 1640 Smith 5 100 Robertson 6 50 Williamson 7 150 Smith 8 250 Smith 9 840 Brown 10 440 Black 11 20 Brown sqlite>
五、 限制返回数量 SELECT 列... FROM 表 LIMIT 数量 OFFSET 位置
有时候数据库中的数据太多，全部返回可不行，可以限制返回的数量，还可以设定返回的起始位置，如下：
sqlite> sqlite> SELECT * FROM Cars LIMIT 4; Id Name Cost ---- --------------- --------------- 1 Audi 52642 2 Mercedes 57127 3 Skoda 9000 4 Volvo 29000 sqlite> sqlite> SELECT * FROM Cars LIMIT 4 OFFSET 2; Id Name Cost ---- --------------- --------------- 3 Skoda 9000 4 Volvo 29000 5 Bentley 350000 6 Citroen 21000 sqlite>
六、 别名 SELECT 列 AS 别名，列 AS 别名 FROM
我们可以给返回数据集中的某些列起一个比较直观的名字，比如把 Cost 改为"Price Of Car"
sqlite> sqlite> SELECT Name , Cost AS 'Price Of Car' FROM Cars; Name Price Of Car ---- --------------- Audi 52642 Merc 57127 Skod 9000 Volv 29000 Bent 350000 Citr 21000 Humm 41400 Volk 21600 sqlite>
七、 条件查询 SELECT 列 FROM 表 【WHERE 条件语句】
一般的条件语句都是大于、小于、等于之类的，这里有几个特别的条件语句
LIKE
- LIKE 用通配符匹配字符串
- 下划线 _ 匹配一个字符串
- 百分号 % 匹配多个字符串
- LIKE 匹配字符串时不区分大小写
sqlite> sqlite> SELECT * FROM Cars WHERE Name Like '____'; Id Name Cost ---- --------------- --------------- 1 Audi 52642 sqlite> sqlite> SELECT * FROM Cars WHERE Name Like '%en'; Id Name Cost ---- --------------- --------------- 6 Citroen 21000 8 Volkswagen 21600 sqlite> sqlite> SELECT * FROM Cars WHERE Name Like '%EN'; Id Name Cost ---- --------------- --------------- 6 Citroen 21000 8 Volkswagen 21600 sqlite>
GLOB
- GLOB 用通配符匹配字符串
- 下划线 ? 匹配一个字符串
- 百分号 * 匹配多个字符串
- LIKE 匹配字符串时,区分大小写
BETWEEN 值1 AND 值2
返回两个值之间的数据集合。下面的语句查询价格在 20000 到 55000 之间的车，都是好车啊。
sqlite> sqlite> SELECT * FROM Cars WHERE Cost BETWEEN 20000 AND 55000; Id Name Cost ---- --------------- --------------- 1 Audi 52642 4 Volvo 29000 6 Citroen 21000 7 Hummer 41400 8 Volkswagen 21600 sqlite>
IN （集合）
对应列的值必须在集合中。下面的语句查找奥迪和悍马的价格。
sqlite> sqlite> SELECT * FROM Cars WHERE Name IN ('Audi','Hummer'); Id Name Cost ---- --------------- --------------- 1 Audi 52642 7 Hummer 41400 sqlite>
八、 排序 ORDER BY 列 ASC (DESC)
指定某个列进行排序，ASC 为升序，DESC 为降序。下面的语句查询汽车品牌和价格，并以价格排序
sqlite> sqlite> SELECT Name, Cost FROM Cars ORDER BY Cost DESC; Name Cost ---- --------------- Bent 350000 Merc 57127 Audi 52642 Humm 41400 Volv 29000 Volk 21600 Citr 21000 Skod 9000 sqlite>
九、 区分 DISTINCT 列
有一些字段的值可能会出现重复，比如订单表中，一个客户可能会有好几份订单，因此客户的名字会重复出现。
到底有哪些客户下了订单呢？下面的语句将客户名字区分出来。
sqlite> sqlite> Select * FROM Orders; Id OrderPrice Customer ---- --------------- --------------- 1 1200 Williamson 2 200 Robertson 3 40 Robertson 4 1640 Smith 5 100 Robertson 6 50 Williamson 7 150 Smith 8 250 Smith 9 840 Brown 10 440 Black 11 20 Brown sqlite> sqlite> SELECT DISTINCT Customer FROM ORDERS; Customer --------------- Black Brown Robertson Smith Williamson sqlite>
十、 分组 GROUP BY 列
分组和前面的区分有一点类似。区分仅仅是为了去掉重复项，而分组是为了对各类不同项进行统计计算。
比如上面的例子，我们区分出 5 个客户，这 5 个客户一共下了 11 个订单，说明很多客户都下了不止一个订单。
下面的语句统计每个客户在订单上总共花费了多少钱。
sqlite> sqlite> SELECT sum(OrderPrice) AS Total, Customer FROM Orders GROUP BY Customer; Total Customer --------------- --------------- 440 Black 860 Brown 340 Robertson 2040 Smith 1250 Williamson sqlite>
这里 Sum 是 SQLite 内置的统计函数，在这个例子中用来求每个顾客的订单价格的和。
统计结果也可以设定返回条件，但是不能用 WHERE 子句，而是用 HAVING 子句，如下例，返回订单总额大于 1000 的顾客。
sqlite> sqlite> SELECT sum(OrderPrice) AS Total, Customer FROM Orders ...> GROUP BY Customer HAVING sum(OrderPrice)>1000; Total Customer --------------- --------------- 2040 Smith 1250 Williamson sqlite>
十一、 逻辑运算符
有的查询涉及的条件语句很复杂，是有好几个条件语句经过逻辑运算得来的，一共有三种逻辑运算符：
- AND
- OR
- NOT
一般稍微了解点编程知识的应该都没问题。
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