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- What are the sql commands to delete tables?
- SQL commands to delete tables: 1. drop, deletes content and definitions, and releases space; 2. truncate, deletes content, releases space but does not delete definitions; 3. delete statement is used to delete rows in the table; 4. truncate table deletes the table All rows in , but the table structure and its columns, constraints, indexes, etc. remain unchanged.
- SQL 35087 2020-10-30 14:15:48
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- How to start sql server service
- How to start the sql server service: 1. Click the start menu and find the sql server folder; 2. Open [Configuration Tools] and [sql server configuration manager] in sequence; 3. Right-click the sql server service and click [Start] .
- SQL 14051 2020-10-30 16:57:26
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- What are the common SQL query statements?
- Common SQL query statements include: 1. View table structure [SQL>DESC emp;]; 2. Query all columns [SQL>SELECT * FROM emp]; 3. Query specified columns [SQL>SELECT empmo,]; 4. Query Specify the row [SQL>SELECT * FROM].
- SQL 10248 2020-10-26 15:31:41
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- How to remove duplicate queries in sql
- SQL deduplication query method: Duplicate records are judged based on a single field peopleId, and deleted using the statement, the code is [where peopleId in (select peopleId from people group by peopleId].
- SQL 16067 2020-10-10 11:37:29
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- What is the function of where phrase in sql command?
- The function of the where phrase in the sql command is to specify the selection criteria and filter records; if you need to conditionally select data from the table, you can add the WHERE clause to the SELECT statement.
- SQL 10545 2020-08-31 17:10:21
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- What is a description of how a database is physically stored called?
- The description of how a database is physically stored is called the "internal schema". The internal schema gives the physical storage structure and physical access methods of the database, such as the file structure, index, clustering, hash and other access methods and access paths of data storage. The physical properties of the internal schema are mainly reflected in the operating system and file level. superior.
- SQL 11940 2020-08-31 16:29:51
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- What is the operation called to find tuples that satisfy a given condition from a relation in a relational database?
- In a relational database, finding tuples that satisfy a given condition from a relationship is called selection. The condition is given as a logical expression, and the tuple with a true value will be selected.
- SQL 19044 2020-08-31 16:11:26
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- What software is used to implement various data operations in the database?
- The software used to implement various data operations in the database is: database management system; the database management system can directly operate the data in the database. Database management system is a large-scale software that manipulates and manages databases and is used to establish, use and maintain databases; it provides unified management and control of databases to ensure the security and integrity of the databases.
- SQL 16212 2020-08-29 15:25:06
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- What three common functions does the sql language have?
- The three common functions of SQL language are: 1. Data definition; it can define the three-level schema structure of the database, namely external schema, global schema and internal schema structure. 2. Data manipulation; including data insertion, deletion, modification and query functions for basic tables and views. 3. Data control; mainly controlling user access rights to ensure system security.
- SQL 37437 2020-08-29 13:46:01
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- SQL server high concurrency generates unique order number
- We can use stored procedures and data tables to build a table and create stored procedures. The stored procedure is responsible for generating order numbers, and the table is responsible for handling uniqueness issues.
- SQL 2896 2020-08-29 12:01:38
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- What are the two categories of data operations in relational databases?
- Data operations in relational databases are divided into two categories: query and update. Query statements are used for various retrieval operations, and update operations are used for operations such as insertion, deletion, and modification.
- SQL 12220 2020-08-29 11:32:28
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- When creating a crosstab query, where does the value of the column header field appear in the crosstab?
- When you create a crosstab query, the value of the column header field appears in the crosstab at the first row. A crosstab query groups the fields from a table. One group of columns is on the left side of the data table as the row fields of the crosstab, and the other group of columns is on the top of the data table as the column fields of the crosstab.
- SQL 10520 2020-08-29 11:32:12
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- What is the syntax structure of select statement in SQL?
- The syntax structure of the select statement in SQL is: "SELECT select_list [ INTO..] FROM table_name [ WHERE...] [ GROUP BY...][ HAVING...][ ORDER BY...];".
- SQL 12053 2020-08-29 11:30:46
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- What are the commonly used methods for sql optimization?
- Commonly used methods for sql optimization include: 1. Try to avoid full table scans, and consider establishing indexes on the columns involved in where and order by; 2. Try to avoid making null value judgments on fields in the where clause; 3. Use with caution in and not in; 4. Try to avoid large transaction operations and improve system concurrency.
- SQL 8402 2020-08-24 13:12:38
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- Why does invalid column index appear in sql
- Reasons for invalid column index in sql: 1. The placeholder is inconsistent with the number of parameters; 2. SQL splicing error, please note that each [%] must be included with [''], and spliced with the parameters with [||]; 3 , wrong annotation.
- SQL 6351 2020-08-22 10:07:06
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