如果你每次建数据表的时候固执的使用varchar,那么你可能会遇到以下的问题:
现在saleUserName的字段类型为varchar(50)
update TableNameset saleUserName='小覃祝你⑭快乐' where ID=87
select * from TableName where ID=87
why?SaleUserName字段里的文字怎么变成这样了。⑭这个符号怎么变成了?
好的,那么我现在将saleUserName的字段类型改为nvarchar(50)呢
updateTableNameset saleUserName='小覃祝你⑭快乐' where ID=87
select * from TableName where ID=87
What!?怎么还是一样!
那么,稍微改一下,在参数值前面加上N。现在可以看到调皮的⑭出来了。
updateTableNameset saleUserName=N'小覃祝你⑭快乐' where ID=87
------加上N代表存入数据库时以Unicode格式存储。
----------------------------------------------------------总结的时候,我总是得召唤出这么华丽的分割线-----------------------------------------------------------------
unicode,以前学习的时候看过,根本没留心。那么好,百度一下,百度百科是这么说的:Unicode是国际组织制定的可以容纳世界上所有文字和符号的字符编码方案。
nvarchar和ntext就是可以容纳unicode的类型,所以才能存储调皮的⑭等特殊字符。
以前根本没留意过这些数据类型,看到说是存unicode类型的,可是根本不知道unicode为何物。码农就是这么任性,不够重视这些东西。

ACID attributes include atomicity, consistency, isolation and durability, and are the cornerstone of database design. 1. Atomicity ensures that the transaction is either completely successful or completely failed. 2. Consistency ensures that the database remains consistent before and after a transaction. 3. Isolation ensures that transactions do not interfere with each other. 4. Persistence ensures that data is permanently saved after transaction submission.

MySQL is not only a database management system (DBMS) but also closely related to programming languages. 1) As a DBMS, MySQL is used to store, organize and retrieve data, and optimizing indexes can improve query performance. 2) Combining SQL with programming languages, embedded in Python, using ORM tools such as SQLAlchemy can simplify operations. 3) Performance optimization includes indexing, querying, caching, library and table division and transaction management.

MySQL uses SQL commands to manage data. 1. Basic commands include SELECT, INSERT, UPDATE and DELETE. 2. Advanced usage involves JOIN, subquery and aggregate functions. 3. Common errors include syntax, logic and performance issues. 4. Optimization tips include using indexes, avoiding SELECT* and using LIMIT.

MySQL is an efficient relational database management system suitable for storing and managing data. Its advantages include high-performance queries, flexible transaction processing and rich data types. In practical applications, MySQL is often used in e-commerce platforms, social networks and content management systems, but attention should be paid to performance optimization, data security and scalability.

The relationship between SQL and MySQL is the relationship between standard languages and specific implementations. 1.SQL is a standard language used to manage and operate relational databases, allowing data addition, deletion, modification and query. 2.MySQL is a specific database management system that uses SQL as its operating language and provides efficient data storage and management.

InnoDB uses redologs and undologs to ensure data consistency and reliability. 1.redologs record data page modification to ensure crash recovery and transaction persistence. 2.undologs records the original data value and supports transaction rollback and MVCC.

Key metrics for EXPLAIN commands include type, key, rows, and Extra. 1) The type reflects the access type of the query. The higher the value, the higher the efficiency, such as const is better than ALL. 2) The key displays the index used, and NULL indicates no index. 3) rows estimates the number of scanned rows, affecting query performance. 4) Extra provides additional information, such as Usingfilesort prompts that it needs to be optimized.

Usingtemporary indicates that the need to create temporary tables in MySQL queries, which are commonly found in ORDERBY using DISTINCT, GROUPBY, or non-indexed columns. You can avoid the occurrence of indexes and rewrite queries and improve query performance. Specifically, when Usingtemporary appears in EXPLAIN output, it means that MySQL needs to create temporary tables to handle queries. This usually occurs when: 1) deduplication or grouping when using DISTINCT or GROUPBY; 2) sort when ORDERBY contains non-index columns; 3) use complex subquery or join operations. Optimization methods include: 1) ORDERBY and GROUPB


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