mysql基本语法

Posted 2021-03-07 biglayman

union和union all

-- 查询t_book的id
SELECT id FROM t_book;
-- 查询t_booktype的id
SELECT id FROM t_booktype;
-- union查询去重
SELECT id FROM t_book UNION SELECT id FROM t_booktype;
-- union all简单重复
SELECT id FROM t_book UNION ALL SELECT id FROM t_booktype;

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使用别名查询，方便书写

-- 使用别名查询
SELECT * FROM t_book WHERE id=1;
SELECT * FROM t_book t WHERE t.id=1;
SELECT t.bookName FROM t_book t WHERE t.id=1;
SELECT t.bookName bName FROM t_book t WHERE t.id=1;
SELECT t.bookName AS bName FROM t_book t WHERE t.id=1;

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插入几条样例记录，方便更新和删除

INSERT INTO t_book VALUES(NULL,‘我爱我家‘,20,‘张三‘,1);

INSERT INTO t_book(id,bookName,price,author,bookTypeId) VALUES(NULL,‘我爱我家‘,20,‘张三‘,1);

INSERT INTO t_book(bookName,author) VALUES(‘我爱我家‘,‘张三‘);

INSERT INTO t_book(id,bookName,price,author,bookTypeId) VALUES (NULL,‘我爱我家2‘,20,‘张三‘,1),(NULL,‘我爱我家3‘,20,‘张三‘,1);

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-- 根据主键更新记录
UPDATE t_book SET bookName=‘Java编程思想‘,price=120 WHERE id=1;
-- 根据模糊条件跟新记录
UPDATE t_book SET bookName=‘我‘ WHERE bookName LIKE ‘%我爱我家%‘;
-- 根据主键删除记录
DELETE FROM t_book WHERE id=5;
-- 根据条件删除记录
DELETE FROM t_book WHERE bookName=‘我‘;

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基本的索引

-- 创建普通索引
CREATE TABLE t_user1(id INT ,
                     userName VARCHAR(20),
                     PASSWORD VARCHAR(20),
                     INDEX (userName)
                 );
-- 创建唯一性索引                 
CREATE TABLE t_user2(id INT ,
                     userName VARCHAR(20),
                     PASSWORD VARCHAR(20),
                     UNIQUE INDEX index_userName(userName)
                 );
-- 创建全文索引               
CREATE TABLE t_user3(id INT ,
                     userName VARCHAR(20),
                     PASSWORD VARCHAR(20),
                     INDEX index_userName_password(userName,PASSWORD)
                 );
-- 创建单列索引                 
CREATE     INDEX index_userName ON t_user4(userName);
-- 创建多列索引
CREATE     UNIQUE INDEX index_userName ON t_user4(userName);
-- 创建空间索引
CREATE  INDEX index_userName_password ON t_user4(userName,PASSWORD);
-- 在已经存在的表上创建索引
ALTER TABLE t_user5 ADD INDEX index_userName(userName);
-- 使用ALTER TABLE 语句来创建索引
ALTER TABLE t_user5 ADD UNIQUE INDEX index_userName(userName);
ALTER TABLE t_user5 ADD INDEX index_userName_password(userName,PASSWORD);
-- 删除索引
DROP INDEX index_userName ON t_user5;

DROP INDEX index_userName_password ON t_user5;

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视图

-- 创建视图
CREATE VIEW v1 AS SELECT * FROM t_book;

CREATE VIEW v2 AS SELECT bookName,price FROM t_book;

CREATE VIEW v3(b,p) AS SELECT bookName,price FROM t_book;


SELECT * FROM v1;

SELECT * FROM v2;

SELECT * FROM v3;
-- 在多表上创建视图
CREATE VIEW v4 AS SELECT bookName,bookTypeName FROM t_book,t_booktype WHERE t_book.bookTypeId=t_booktype.id;

CREATE VIEW v5 AS SELECT tb.bookName,tby.bookTypeName FROM t_book tb,t_booktype tby WHERE tb.bookTypeId=tby.id;

SELECT * FROM v4;

SELECT * FROM v5;
-- 语句查看视图基本信息
DESC v5;
SHOW TABLE STATUS LIKE ‘v5‘;
SHOW TABLE STATUS LIKE ‘t_book‘;
-- 语句查看视图详细信息
SHOW CREATE VIEW v5;

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触发器

-- 一个执行语句的触发器
CREATE TRIGGER trig_book AFTER INSERT 
     ON t_book FOR EACH ROW
        UPDATE t_bookType SET bookNum=bookNum+1 WHERE new.bookTypeId=t_booktype.id;
        
-- 显然这里主键不能为空      
INSERT INTO t_book VALUES(NULL,‘java好‘,100,‘ke‘,1);

-- DELIMITER是用来执行整条语句的
DELIMITER |
CREATE TRIGGER trig_book2 AFTER DELETE 
    ON t_book FOR EACH ROW
    BEGIN
       UPDATE t_bookType SET bookNum=bookNum-1 WHERE old.bookTypeId=t_booktype.id;
       INSERT INTO t_log VALUES(NULL,NOW(),‘在book表里删除了一条数据‘);
       DELETE FROM t_test WHERE old.bookTypeId=t_test.id;
    END 
|
DELIMITER ;
-- 删记录
DELETE FROM t_book WHERE id=5;
-- 查看触发器记录
SHOW TRIGGERS;
-- 删触发器
DROP TRIGGER trig_book2 ;

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博客使用的mysql实例均来自http://www.java1234.com/