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- What is used to represent entities in the access database
- Records are used to represent entities in the access database. A record represents an entity, and a field can only represent a certain attribute of the entity. Access has four functional areas by default: Start, Create, External Data and Database Tools.
- SQL 16979 2020-07-08 10:20:37
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- What is the attribute or combination of attributes that can uniquely identify a tuple in the database called?
- An attribute or combination of attributes that can uniquely identify a tuple in the database is called a key. A database is a warehouse that stores data. It has a large storage space and can store a lot of data. But the database does not store data randomly, there are certain rules.
- SQL 27578 2020-07-08 09:58:37
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- What is the use of 'where 1=1' in SQL?
- In fact, 1=1 is eternally true and means unconditional, which means that it does not matter whether there is 1=1 in the SQL statement. This 1=1 is often used when applications piece together where conditions based on different user selections.
- SQL 8938 2020-07-07 15:59:46
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- How to update one table with another table through SQL statement
- How to update one table with another table through SQL statements: You can use the SELECT INTO statement. For example, [update visit set visit.nm = user.nm from user where visit.uid = user.uid].
- SQL 14740 2020-07-07 11:50:42
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- What are the six database objects?
- Database objects include: users (people who have permission to access the database), views (display the data items required by the user), indexes (providing users with a way to quickly access data), triggers (a collection of user-defined SQL transaction commands), and sequences. (providing a sequence table of unique values), chart (a schematic diagram of the relationship between database tables).
- SQL 37124 2020-07-07 11:03:41
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- What is the relationship between tables and databases in access?
- The relationship between tables and databases in access is: a database can contain multiple tables. Access is a database management system that manages information through various database objects; these objects are all stored in the same database file. A database can have multiple tables, and tables can have relationships or be independent of each other.
- SQL 21902 2020-07-06 16:57:37
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- What is the difference between sql left join and right join?
- The difference between sql left connection and right connection is that the left connection will read all the data in the left data table, even if the right data table does not have corresponding data; while the right connection will read all the data in the right data table, even if the left data table does not have corresponding data.
- SQL 8545 2020-07-06 16:17:57
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- What are the three most commonly used Chinese databases?
- The three most commonly used Chinese databases are: "MySQL", "SQL Server", and "Oracle". "MySQL" has the characteristics of small size and low cost; "SQL Server" has the characteristics of ease of use and friendly user interface; "Oracle" has the characteristics of good system portability, fast and flexible.
- SQL 25280 2020-07-06 15:43:23
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- How many primary keys are there in a single data table of the database?
- There can be only one primary key in a single data table of the database. A database primary key refers to a column or a combination of multiple columns, whose value can uniquely identify each row in the table, through which the entity integrity of the table can be enforced; the primary key is mainly used to associate foreign keys with other tables, as well as this Modification and deletion of records.
- SQL 14677 2020-07-06 15:20:00
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- What database language does sql belong to?
- SQL is a relational database language. Relational database language is a database language with multiple functions such as data manipulation and data definition. This language has interactive characteristics, can provide users with great convenience, and can use SQL language to improve the work quality and performance of computer application systems. efficiency.
- SQL 16252 2020-07-06 16:18:34
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- What are the applications of database management systems?
- Applications of database management systems: 1. Improve the security of data encryption systems; 2. Improve information storage efficiency; 3. Improve data backup and recovery; 4. Enhance multimedia management. The database management system provides unified management and control of the database to ensure the security and integrity of the database.
- SQL 9116 2020-07-04 10:10:57
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- The role of database index
- The biggest function of a database index is to speed up queries. It can fundamentally reduce the number of record rows that need to be scanned. A database index is the data structure of the database. Furthermore, the data structure stores all the values of a certain column in a table. , that is to say, the index is created based on a certain column in the data table.
- SQL 8657 2020-07-03 17:19:44
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- What are the SQL statements to delete fields in a table?
- SQL statements to delete fields in the table include: 1. Delete columns without default values [alter table Test drop COLUMN BazaarType]; 2. Delete columns with default values [alter table Test DROP COLUMN BazaarType].
- SQL 15411 2020-07-03 16:20:48
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- What is the sql statement to modify the table name?
- The SQL statement to modify the table name is the "ALTER TABLE" statement; the basic syntax is: "ALTER TABLE <table name> [modification options]". The "ALTER TABLE" statement is used to modify the design of an existing table; columns can be added, modified, or deleted from an existing table.
- SQL 32870 2020-07-03 16:00:45
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- What are the SQL date format conversion functions?
- The sql date format conversion functions are: 1. [Select CONVERT(GETDATE(), 23)] formats the current date into [year-month-day] format; 2. [Select CONVERT(GETDATE(), 8] formats the current time Format it into [hour:minute:second] format.
- SQL 14017 2020-07-03 11:33:47
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