在写查询功能的过程中遇到一个这样的问题:按日期范围查询,sql语句是:where dt=用户选择起始日期dt=用户选择结束日期。数据库中的数据如图1,我选择的测试数据起始时间是2008-01-06结束日期是2009-06-01。期望的结果应该能查出第一条数据。执行sql语句并无
在写查询功能的过程中遇到一个这样的问题:按日期范围查询,sql语句是:where dt>=用户选择起始日期&&dt
图1
这时的解决办法是把数据库中数据的格式更改为YYYY-MM-dd。问题来了。
用户用的数据库是Sqlserver,因开发需要我们公司用的是Sqlite数据库,需要将用户的Sqlserver数据表导入到我们的Sqlite数据库。SqlServer数据库中时间格式是YYYY-MM-dd HH:mm:ss(SqlServer数据库会把插入的datetime类型数据自动规范成YYYY-MM-dd HH:mm:ss类型)导入时我选择的是Navicat Premium工具。导入数据成功,在Sqlite中打开数据表时发现表中数据是YYYY-M-d格式。原因是Sqlite数据库不支持datetime类型的数据,因此数据库中dt是Text类型,不能像Sqlite那样自动规范日期字段格式。如图1:Sqlite中数据是2009-6-1没有补0,测试数据选择的结束日期2009-06-01,比较时6>0,所以数据库第一条数据没有查询出来。
解决办法是:先把SqlServer中的数据导入到Excel中,再把.xls导入到Sqlite数据库。
1.把SqlServer中的数据导入到Excel中。导入之前先新建一个Excel文档,把数据库中的字段名写到第一行作为列头(即把此文档作为数据导入的模板)如图2。导出时使用SqlServer自带的导出数据功能,具体方法不再详细叙述。在选择目标时,Excel文件路径选择建好的Excel文档,首行包含列名称项可选可不选如图3。
图2 图3
注意:如果不在导出之前写上列头建好Excel模板,导出时会报错如图4。如果导出的日期时间仍不会补0,尝试新建Excel模板,选中日期列右键设置单元格格式为文本,然后重复以上步骤。
图4
2.最后将导出成功的Excel文档导入到Sqlite数据库,使用Navicat Premium工具即可做到,使用该工具导入时可选择日期时间类型数据的分隔符是-还是/。具体导入方法不再叙述。

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MySQL is suitable for beginners to learn database skills. 1. Install MySQL server and client tools. 2. Understand basic SQL queries, such as SELECT. 3. Master data operations: create tables, insert, update, and delete data. 4. Learn advanced skills: subquery and window functions. 5. Debugging and optimization: Check syntax, use indexes, avoid SELECT*, and use LIMIT.

MySQL efficiently manages structured data through table structure and SQL query, and implements inter-table relationships through foreign keys. 1. Define the data format and type when creating a table. 2. Use foreign keys to establish relationships between tables. 3. Improve performance through indexing and query optimization. 4. Regularly backup and monitor databases to ensure data security and performance optimization.

MySQL is an open source relational database management system that is widely used in Web development. Its key features include: 1. Supports multiple storage engines, such as InnoDB and MyISAM, suitable for different scenarios; 2. Provides master-slave replication functions to facilitate load balancing and data backup; 3. Improve query efficiency through query optimization and index use.

SQL is used to interact with MySQL database to realize data addition, deletion, modification, inspection and database design. 1) SQL performs data operations through SELECT, INSERT, UPDATE, DELETE statements; 2) Use CREATE, ALTER, DROP statements for database design and management; 3) Complex queries and data analysis are implemented through SQL to improve business decision-making efficiency.

The basic operations of MySQL include creating databases, tables, and using SQL to perform CRUD operations on data. 1. Create a database: CREATEDATABASEmy_first_db; 2. Create a table: CREATETABLEbooks(idINTAUTO_INCREMENTPRIMARYKEY, titleVARCHAR(100)NOTNULL, authorVARCHAR(100)NOTNULL, published_yearINT); 3. Insert data: INSERTINTObooks(title, author, published_year)VA


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