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- What is the sql modification statement?
- The sql modification statement is an UPDATE statement. The UPDATE statement is used to update existing records in the table. Please pay attention to the WHERE clause in the SQL UPDATE statement! The WHERE clause specifies which record or records need to be updated. If you omit the WHERE clause, all records will be updated!
- SQL 8228 2019-06-18 14:37:28
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- What is the database add statement?
- The database add statement is the INSERT INTO statement. The INSERT INTO statement is used to insert new records into the table. The INSERT INTO statement can be written in two forms: the first form does not need to specify the column name of the data to be inserted, and only needs to provide the inserted value; the second form requires Specify the column name and the value to be inserted.
- SQL 30076 2019-06-18 14:39:04
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- A brief discussion of database stored procedures
- Database stored procedures: Stored procedures are methods, with similar method names, variables to be passed by the method, and return results, so stored procedures have stored procedure names, stored procedure parameters, and return values.
- SQL 40523 2020-09-12 14:54:54
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- Detailed explanation of database stored procedures
- Stored procedures can be viewed as stored t-sql scripts in the database. Why use stored procedures? 1. Increase performance; 2. Enhance security; 3. Use non-database technology in transact-sql; 4. Programming mode - use external programming language calls.
- SQL 14848 2019-06-20 14:16:12
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- What are the two methods of database backup?
- The two methods for database backup are: 1. Use mysqldump combined with the exec function for database backup; 2. Use the [php+mysql+header] function for database backup.
- SQL 32329 2020-09-12 16:34:30
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- What are the transaction isolation levels of the database?
- In database operations, in order to effectively ensure the correctness of concurrently read data, the transaction isolation level is proposed. A general database includes four isolation levels: read uncommitted, read committed, repeatable read, and serialized; different isolation levels handle transactions differently.
- SQL 25562 2019-06-12 17:08:33
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- What are the commonly used SQL statements?
- Commonly used SQL statements include show databases; create database db1; show create; show tables; database db1; create database db1, etc.
- SQL 5645 2019-06-10 16:38:32
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- what is json
- JSON (JavaScript Object Notation) is a lightweight data exchange format that is easy to read and write, as well as easy to be parsed and generated by machines. .
- SQL 13070 2019-06-17 15:20:37
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- What is the order of sql execution?
- The SQL statement is divided into 11 steps. The FROM operation is always executed first, and the LIMIT operation is executed last. Each operation will generate a virtual table, which is used as an input for processing. However, these virtual tables are transparent to the user, and the last virtual table will be returned as a result.
- SQL 29763 2019-06-17 15:20:50
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- What are the commonly used relational databases?
- Simply put, a relational database is a database composed of multiple two-dimensional row and column tables that can be connected to each other. The current mainstream relational databases include Oracle, DB2, Microsoft SQL Server, Microsoft Access, MySQL, etc.
- SQL 99276 2019-06-06 13:11:10
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- Several methods of sql optimization
- To optimize queries, you should try to avoid full table scans. You should first consider building indexes on the columns involved in where and order by. You should try to avoid using or in the where clause to connect conditions, otherwise the search engine will give up using the index and Perform a full table scan.
- SQL 27432 2019-06-05 16:04:19
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- Database type
- Databases are divided into relational databases and non-relational databases. Commonly used relational databases include MySQL, MariaDB database, SQL Server database, and Access database; commonly used non-relational databases include memcached, Redis, MongoDB, Cassandra, etc.
- SQL 5141 2019-06-05 10:41:49
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- What are the differences between delete and truncate
- The difference between delete and truncate commands: delete is a data manipulation language (DML) command, which uses row-level locking, and can delete single, multiple or all records from the table; while truncate is a data definition language (DDL) command, which uses table-level locking. , delete all records and table structures from the database. etc.
- SQL 43029 2019-06-17 15:31:04
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- Why use redis?
- Redis is an open source log-type, [Key-Value] database written in ANSI C language, supports network, can be memory-based and persistent, and provides APIs in multiple languages; using redis can greatly improve system access efficiency.
- SQL 18852 2020-09-18 10:11:00
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- When do you need to use redis?
- When you need to use redis: 1. Data that does not need to be updated in real time but consumes a lot of database data; 2. Data that needs to be updated in real time, but the update frequency is not high; 3. The number of visits at a certain moment is very high and the updates are also very frequent. data.
- SQL 14601 2020-09-18 10:18:10
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