MySql 基本sql语句

#库操作：
    SHOW DATABASES;#显示所有数据库
    CREATE DATABASE  IF NOT EXISTS db_name CHARACTER SET UTF8; # 创建库(选择字符编码)
    SHOW CREATE DATABASE db_name[CHARACTER SET UTF8];# 查看新建库的方式
    ALTER DATABASE db_name [CHARACTER SET UTF-8]; # 修改数据库
    USE db_name; # 使用数据库
    SELECT DATABASE(); # 查看当前使用的数据库

#表操作：
        SHOW TABLES;

        CREATE TABLE tab_name （field type [完整性约束条件] CHECK (id>0)) [CHARACTER SET UTF-8];
        #创建表
        -- CHECK 为约束，插入更新数据时会检查，保证id是否大于0

        DESC tab_name; # 查看表结构

        RENAME TABLE 旧表名 TO 新表名；# 重命名表

        ALTER TABLE tab_name ADD 列名 type [完整约束条件],
                             ADD 列名 type [完整约束条件];

        ALTER TABLE tab_name DROP 列名；# 删除列

        ALTER TABLE tab_name MODIFY 列名 type [完整约束条件] DEFAULT;

        ALTER TABLE tab_name CHANGE 旧列名 新列名 type；--改列名

        DROP TABLE tab_name；--删表

#注释
/* 注释 */--注释

 #SELECT 语句:
        SELECT DISTINCT name FROM emp; #检索出不同的值(检索多列时若两列不完全相同，
                                                             所有列都会被检索出来)
        SELECT id FROM emp LIMIT 5 OFFSET 5; #检索从第5行起后5行

        ORDER BY:
            SELECT prod_id,prod_price,prod_name
            FROM Products
            ORDER BY prod_price,prod_name;
            -- 仅在prod_price出现相同的值时，才会对prod_name进行排序，如果prod_price的值唯一
            --则不会对prod_name排序

            SELECT prod_id,prod_price,prod_name
            FROM Products
            ORDER BY 2,3;
            -- 先对第2个列进行排序，再对第三个列进行排序

            SELECT prod_id,prod_price,prod_name
            FROM Products
            ORDER BY prod_price DESC,prod_name;
            --有DESC的进行升序排列,默认排列为A到Z (ASC)

            SELECT prod_name as name FROM Product;
            --SELECT指定别名或进行运算都不会改动原表

        WHERE:
            SELECT vend_id,prod_name
            FROM Products
            WHERE vend_id <> ‘DLL01‘;
            --检索除DLL01的值
            --进行不匹配，匹配检索时，null值不会出现在检索结果之中

            SELECT vend_id,prod_name
            FROM Products
            WHERE NOT vend_id = ‘DLL01‘;

            SELECT prod_name,prod_price
            FROM Products
            WHERE prod_price BETWEEN 5 AND 10;--范围检查

            SELECT prod_name,prod_price
            FROM Products
            WHERE prod_price IS NULL;--检索空值

            SELECT vend_id,prod_price,prod_name
            FROM Products
            WHERE vend_id = ‘DLL01‘ AND prod_price <=4;
            -- ORDER BY 子句应在WHERE之后

            SELECT prod_name,prod_price
            FROM Products
            WHERE (vend_id = ‘DLL01‘ OR vend_id = ‘BRS01‘) AND prod_price >= 10;
            --AND的优先级比OR高，一般要用圆括号分组

        --过滤：
                SELECT prod_name,prod_price
                FROM Products
                WHERE vend_id IN (‘DLL01‘,‘BRS01‘)
                ORDER BY prod_name;

                SELECT vend_id,prod_name
                FROM Products
                WHERE prod_name LIKE ‘Fish%‘;
                --检索prod_name中以Fish开头的值（区分大小写），但不会检索出NULL的行
                --还可以这样用：‘%fish%‘

                SELECT vend_id,prod_name
                FROM Products
                WHERE prod_name LIKE ‘_inch teddy bear‘;
                -- 下划线也是通配符，匹配一个字符

        --函数：
                SELECT Concat(vend_name,‘(‘,RTRIM(vend_country),‘)‘) --合并
                AS vend_title               -- 去掉右边的空格
                FROM Vendors ORDER BY vend_name; -- LTRIM()去掉左边的空格，TRIM()去两边

                SELECT quantity*item_price AS expanded_price
                FROM OrderItems
                WHERE order_num = 20008;

                SELECT cust_name,cust_contant FROM Customers
                WHERE SOUNDEX(cust_contact)=SOUNDEX(‘Michael Green‘); --拟声

                SELECT order_num
                FROM Orders
                WHERE YEAR(order_date) = 2012;

        #GROUP BY:
                SELECT vend_id ,COUNT(*) AS num_prods
                FROM Products
                GROUP BY vend_id; -- 要在WHERE子句之后，ORDER BY子句之前
                                  -- GROUP BY 后记得 ORDER BY

                HAVING -- 过滤组：
                    SELECT  cust_id,COUNT(*) AS orders
                    FROM Orders
                    GROUP BY cust_id
                    HAVING orders >=2;

                    SELECT vend_id,COUNT(*) AS num_prods
                    FROM Products
                    WHERE prod_price >=4
                    GROUP BY vend_id
                    HAVING num_prods >=2;
        --子查询：
                -- 策略：看最后一个WHERE 和各个SELECT前的检索值
                 SELECT cust_name,cust_contact
                 FROM Customers
                 WHERE cust_id IN (SELECT cust_id
                                   FROM Orders
                                   WHERE order_num IN (SELECT order_num
                                                       FROM OrderItems
                                                       WHERE prod_id = ‘RGAN01‘));
                                   -- 还可通过联结进行查询
                 SELECT cust_name,
                        cust_state,
                        (SELECT COUNT(*)
                         FROM Orders
                         WHERE Orders.cust_id = Customers.cust_id)
                         AS orders
                 FROM  Customers
                 ORDER BY cust_name;

        --联结表：
            --内联结：
                --内联结就是将两个表并在一起，将两表中的信息同时检索出来
                SELECT vend_name,prod_name,prod_price
                FROM vendors INNER JION Products
                ON Vendors.vend_id = Products.vend_id; --‘标准写法‘

                SELECT prod_name,vend_name,prod_price,quantity
                FROM OrderItems,Products,Vendors
                WHERE Products.vend_id = Vendors.vend_id
                AND OrderItems.prod_id  = Products.prod_id
                AND order_num = 20007; --联结三张表

                SELECT cust_name,cust_contact
                FROM Customers AS C,Orders AS O,OrderItems AS OI
                WHERE C.cust_id = O.cust_id
                AND OI.order_num = O.order_num
                AND prod_id = ‘RGAN01‘

            --自联结:
                SELECT C1.cust_id,C1.cust_name,C1.cust_contact
                FROM  Customers AS C1,Customers AS C2
                WHERE C1.cust_name = C2.cust_name
                AND C2.cust_contact = ‘Jim Jones‘

            --外联结:
                --包含了那些联结表中没有关联的行，叫外联结
                SELECT C.cust_id,O.order_num
                FROM Customers AS C LEFT OUTER JOIN Orders AS O
                ON C.cust_id = O.cust_id;
                -- LEFT OUTER 指左边未关联的行，RIGHT 为右边

                SELECT C.cust_id,
                       COUNT(O.order_num) AS num_ord
                FROM Customers AS C LEFT OUTER JOIN Orders AS O
                ON C.cust_id = O.cust_id
                GROUP BY C.cust_id;

        --组合查询：
                --将多条SELECT语句的查询结果按一个结果返回
                --常用于不同表之间的查询
                --UNION ALL 返回所有行（包括重复的)
                SELECT cust_name,cust_contact,cust_email
                FROM Customers
                WHERE cust_state IN (‘IN‘,‘IL‘,‘MI‘)
                UNION
                SELECT cust_name,cust_contact,cust_email
                FROM Customers
                WHERE cust_name = ‘Fun4All‘
                ORDER BY cust_name --ORDER BY 语句必须放在最后一个SELECT语句后

--插入数据：
        INSERT INTO emp (name,department)
        VALUES("远东","销售部"),("安发","财政部");

        INSERT INTO emp
        SET name="hzw"; # 插入表记录


        INSERT INTO Customers(cust_id)
        SELECT cust_id
        FROM CustNew --导入数据

        SELECT *
        INTO CustCopy
        FROM Customers;--导出数据

        CREATE TABLE CustCopy AS
        SELECT * FROM Customers;
        --运行中创建的表CustCopy将与Customers一样

--更新与删除：
    --UPDATE 修改列数据，DELETE删除行
        UPDATE emp SET depart = "销售部",
                       age = 18
        WHERE name = "ldy" # 修改表记录,UPDATE只能用SET修改

        DELETE FROM emp; # 删除全部表记录

        DELETE FROM emp WHERE id=1 OR id=2; # 删除两行表记录

        DELETE FROM emp WHERE name ="ldy" AND DEPART = "技术部"; -- 准确删除表记录，安全模式下要加上id>0

        TRUNCATE TABLE emp; --删表(先摧毁再新建一个一模一样的)

--视图：

    CREATE VIEW ProductCustomers AS
    SELECT cust_name,cust_contact,prod_id
    FROM Customers AS C,Orders AS O,OrderItems AS OI
    WHERE C.cust_id = O.cust_id
    AND OI.order_num = O.order_num;

    SELECT cust_name,cust_contact
    FROM ProductCustomers
    WHERE prod_id = ‘RGAN01‘;


--事务处理：
    START TRANSACTION;

    INSERT INTO tab_name (name) values(‘ldy‘);
    SAVEPOINT INSERT1;

    ROLLBACK TO INSERT1; --可回退INSERT,UPDATE,DELETE

    COMMIT TRANSACTION;--提交事务
    --只有提交了事务sql语句才真正生效

--游标：
        DECLARE CustCursor CURSOR
        FOR
        SELECT * FROM Customers
        WHERE cust_email IS NULL --创建游标

        OPEN CURSOR CustCursor --使用游标


#约束条件：
           PRIMARY KEY # 非空且唯一
           UNIQUE # 唯一
           NOT NULL # 不为空
           AUTO_INCREMENT # 自增长
#类型：
    #数字类型: TINYINT,SMALLINT,INT

    #字符串类型：CHAR(2) # 只能存2个字节的字符串
                VARCHAR（20） #存20字节以内的字符串
                BLOB # 2进制字符串
                TEXT #文本字符串
    #时间字符串类型：
            DATA 格式：yyyy-mm-dd
            TIME 格式：hh:mm:ss
            YEAR格式：yyyy
            DATETIME 格式：yyyy-mm-dd hh:mm:ss

--外键：
       CREATE tab_name (
               filed_1 INT PRIMARY KEY
               FOREIGN KEY (filed_1) REFERENCES new_tab_name(filed)
              ) -- new_tab_name 被称为主表，tab_name 为子表
              ENGINE = INNODB;--创建外键,filed_1数据类型必须与new_tab_name(filed)的一致
       ALTER TABLE tab_name
               ADD CONSTRAINT abc
               FOREIGN KEY (filed_1)
               REFERENCES new_tab_name(filed)




#常用函数：
    LEFT()--返回字符串左边的字符
    RIGHT()--返回字符串右边的函数
    LENGTH()--返回字符串的长度
    LOWER(),UPPER()--小写大写
    RTRIM(),LTRIM(),TRIM()--删除空格
    SOUNDEX()--返回字符串的SOUNDEX值  --soundex可将任何文本转换成语音表示字母数字模式的算法
    AVG()--某列平均值
    COUNT()--返回某列行数
    MAX()--返回某列的最大值,用于文本数据时返回最后一行
    MIN()--返回某列的最小值，用于文本数据时返回最前一行，均忽略null值
    SUM()--返回某列之和
    COUNT(*)--对所有行进行计数
    COUNT(column)--对特定列进行计数
    LIMIT 5 --检索5行
    OFFSET 5 -- 从第5行开始检索
    DISTINCT field --返回不同的值
    CURRENT_DATE() --获得系统日期