无详细内容 无 select * from li.books where book_publish_date between '1-2月-2005' and '1-2月-2010';select * from books where book_price between 50 and 60;select * from books where catalog_id in (select catalog_id from catalogs where catalog
select * from li.books where book_publish_date between '1-2月-2005' and '1-2月-2010'; select * from books where book_price between 50 and 60; select * from books where catalog_id in (select catalog_id from catalogs where catalog_name='数据库'); select * from catalogs; ---dual 表 select * from dual; -获取oracle 的系统日期 select sysdate from dual; --为前日期增加10天 select sysdate+10 from dual; select (select from dual)+10 from dual; --日期函数 select add_months(sysdate,4) from dual; select add_months('2-2月-1990',4) from dual; -获取指定月份的最后一天 select last_day(sysdate) from dual; select last_day('2-2月-2014') from dual; ---计算两个月之间相差几个月 select months_between(sysdate,'27-4月-2014') from dual; ----日期的四舍五入 ---按年 select round(sysdate,'year') from dual; --按月 select round(sysdate,'month') from dual; select round((select to_date('1987-4-15','yyyy-MM-dd') from dual),'month') from dual; select to_date('1987-3-1','yyyy-MM-dd') from dual --按周 select round(sysdate,'day') from dual; --next_day 的使用, 获取指定日期的下一天所在的日期 select next_day(sysdate,2) from dual; 下一周的第几天; select next_day('27-8月-2014',2) from dual; --阶段当前日期 --按年 select trunc(sysdate,'year') from dual; --按月 select trunc(sysdate,'month') from dual; --按周 select trunc(sysdate,'day') from dual; --比较一组数字中的最大值 select greatest(12,22,33,13,45,5) from dual; select greatest ( '12-5月-2014', '12-12月-2011', '12-3月-2000' ) from dual; ---字符串函数的使用 --截断字符串(从第N个字符开始截取,截取的长度为M个字符) select substr('helloworld',3,5) from dual; --获取指定字符串中的字符位置 select instr('hello','o') from dual; --获取字符串的长度 select length('liuhuahua') from dual; --转换函数 --将其他类型的数据转为字符串(最常用的是日期转字符串) --日期转字符串 select to_char(sysdate,'yyyy-mm-dd') from dual; select sysdate from dual; --将数字转为字符串 select to_char(9898.33,'$99999.999') from dual; --将其他数据转为日期格式(通常是将字符串转为日期) select to_date('1987-3-1','yyyy-MM-dd') from dual; --日期比大小,获取一组日期的最大值 select greatest( to_date('2024-4-22','yyyy-MM-dd'), to_date('2024-5-1','yyyy-MM-dd'), to_date('2014-12-22','yyyy-MM-dd') ) from dual; select '4'+'5' from dual; select 4+5 from dual; --获取用户的登陆ID select uid from books; select user from dual; --聚合函数 select sum(book_price) from books; select count(book_id) from books; ---oracle的分页显示 select * from (select books.* ,rownum r from books where rownum<=6) where r>2; select books.*, rownum from books where rownum<=5; ---group by select catalog_id from books order by catalog_id; select * from books; ---having select catalog_id,sum(book_price) from books group by catalog_id having sum(book_price)>=100 order by catalog_id;

MySQL'sBLOBissuitableforstoringbinarydatawithinarelationaldatabase,whileNoSQLoptionslikeMongoDB,Redis,andCassandraofferflexible,scalablesolutionsforunstructureddata.BLOBissimplerbutcanslowdownperformancewithlargedata;NoSQLprovidesbetterscalabilityand

ToaddauserinMySQL,use:CREATEUSER'username'@'host'IDENTIFIEDBY'password';Here'showtodoitsecurely:1)Choosethehostcarefullytocontrolaccess.2)SetresourcelimitswithoptionslikeMAX_QUERIES_PER_HOUR.3)Usestrong,uniquepasswords.4)EnforceSSL/TLSconnectionswith

ToavoidcommonmistakeswithstringdatatypesinMySQL,understandstringtypenuances,choosetherighttype,andmanageencodingandcollationsettingseffectively.1)UseCHARforfixed-lengthstrings,VARCHARforvariable-length,andTEXT/BLOBforlargerdata.2)Setcorrectcharacters

MySQloffersechar, Varchar, text, Anddenumforstringdata.usecharforfixed-Lengthstrings, VarcharerForvariable-Length, text forlarger text, AndenumforenforcingdataAntegritywithaetofvalues.

Optimizing MySQLBLOB requests can be done through the following strategies: 1. Reduce the frequency of BLOB query, use independent requests or delay loading; 2. Select the appropriate BLOB type (such as TINYBLOB); 3. Separate the BLOB data into separate tables; 4. Compress the BLOB data at the application layer; 5. Index the BLOB metadata. These methods can effectively improve performance by combining monitoring, caching and data sharding in actual applications.

Mastering the method of adding MySQL users is crucial for database administrators and developers because it ensures the security and access control of the database. 1) Create a new user using the CREATEUSER command, 2) Assign permissions through the GRANT command, 3) Use FLUSHPRIVILEGES to ensure permissions take effect, 4) Regularly audit and clean user accounts to maintain performance and security.

ChooseCHARforfixed-lengthdata,VARCHARforvariable-lengthdata,andTEXTforlargetextfields.1)CHARisefficientforconsistent-lengthdatalikecodes.2)VARCHARsuitsvariable-lengthdatalikenames,balancingflexibilityandperformance.3)TEXTisidealforlargetextslikeartic

Best practices for handling string data types and indexes in MySQL include: 1) Selecting the appropriate string type, such as CHAR for fixed length, VARCHAR for variable length, and TEXT for large text; 2) Be cautious in indexing, avoid over-indexing, and create indexes for common queries; 3) Use prefix indexes and full-text indexes to optimize long string searches; 4) Regularly monitor and optimize indexes to keep indexes small and efficient. Through these methods, we can balance read and write performance and improve database efficiency.


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