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- What does % mean in sql
- % in SQL represents a wildcard character, matching any number of characters in the string, which can appear at the beginning, middle, or end of the string, and is used for pattern matching in the LIKE clause.
- SQL 567 2024-04-28 09:06:11
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- How to solve the problem that the sqlplus command cannot be found
- In order to solve the problem that the SQL*Plus command cannot be found, the following steps can be taken: 1. Check the path to ensure that it is installed in the system path; 2. Set the environment variable ORACLE_HOME to point to the parent directory of the installation directory; 3. Refresh the environment to make the changes Take effect; 4. Verify whether the installation is successful; 5. Check the execution file permissions.
- SQL 754 2024-04-18 17:57:15
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- How sqlplus executes sql files
- Use SQLPlus to execute SQL files to automate database tasks. The steps are as follows: Use the sqlplus command to connect to the database. Use the @ or START command to execute the SQL file. Use the -v option to specify runtime parameters such as bind variables. Use the -l option to redirect output to a log file.
- SQL 623 2024-04-18 17:54:14
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- How to solve garbled code in sqlplus
- SQLPlus garbled characters are caused by character set mismatch. Solution: 1. Set the NLS_LANG environment variable; 2. Use client tools that support character sets; 3. Modify the SQLPlus startup script; 4. Modify the database configuration; 5. Use JDBC connection to explicitly set the character set; ensure that the character set is set in Be consistent across databases, client tools, and code.
- SQL 1123 2024-04-18 17:52:09
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- The use and syntax of sql triggers
- A trigger is a type of database code that automatically executes when a specific event (insert, update, delete) occurs. The trigger syntax includes trigger name, table name, triggering time (BEFORE/AFTER) and event type (INSERT/UPDATE/DELETE). Trigger types include BEFORE and AFTER, and event types include INSERT, UPDATE, and DELETE. Triggers can be used for data integrity verification, audit logging, automated tasks, and business logic. For example, you can create a trigger to record the insertion time when a new row is inserted to ensure data consistency.
- SQL 1114 2024-04-13 14:57:16
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- Three triggering methods of sql trigger
- The triggering methods of SQL triggers are: BEFORE: Triggered before data modification, used to enforce business rules. AFTER INSERT: Triggered after inserting a new row, used to add or update data to other tables. AFTER UPDATE: Triggered after updating an existing row, used to update related tables or record change history.
- SQL 1280 2024-04-13 14:54:18
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- How to import mdf file into sqlserver
- The import steps are as follows: Copy the MDF file to SQL Server's data directory (usually C:\Program Files\Microsoft SQL Server\MSSQL\DATA). In SQL Server Management Studio (SSMS), open the database and select Attach. Click the Add button and select the MDF file. Confirm the database name and click the OK button.
- SQL 1053 2024-04-08 11:41:28
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- How to read data in sql
- To read data using SQL, you can use the SELECT statement, whose basic syntax is: SELECT column name FROM table name; you can specify conditions through the WHERE clause, sort the results with the ORDER BY clause, and limit the number of rows with the LIMIT clause. Advanced options include JOIN, GROUP BY, and HAVING for joining multiple tables, grouping results, and filtering results based on grouping.
- SQL 721 2024-04-02 01:09:19
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- How to read blob in sql
- There are four ways to read BLOB in SQL: read directly as binary data, convert to text or JSON using streaming, use SQL Server's varbinarymax type
- SQL 1174 2024-04-02 01:06:22
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- Basic usage of exists in sql
- EXISTS is a keyword used in SQL to determine whether a subquery returns results. The return value is true or false, indicating whether the subquery has results. The basic syntax is "SELECT column1, column2", column1, column2, ... Yes The column name to be queried.
- SQL 1249 2024-01-26 15:32:46
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- distinct usage in SQL
- DISTINCT in SQL is a keyword used to query unique result sets. It can be used in SELECT statements, COUNT aggregate functions and other statements. The basic syntax is "SELECT DISTINCT column1, column2", where the DISTINCT keyword is placed in the SELECT key After the word, followed by the column name or expression to be queried, separated by commas.
- SQL 3022 2024-01-26 15:14:14
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- How to use distinct in SQL
- The DISTINCT keyword in SQL is used to remove duplicate rows from query results. It can be applied to one or more columns in the SELECT statement to return a unique value combination. The usage method is "SELECT DISTINCT column1, column2, ..." The DISTINCT keyword acts on all specified columns. If multiple columns are combined to produce different results, then these rows will also be considered different and will not be deduplicated.
- SQL 2591 2024-01-25 11:52:51
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- What are the differences between database views and tables?
- The differences between database views and tables are: 1. A table is a physical structure used to store data in a database, while a view is just a query result set based on a table or multiple tables; 2. A table is the physical storage unit of data, and a view only provides Rules for viewing and operating table data; 3. Views provide an advanced security mechanism for the database, and tables have no security mechanism; 4. Views are abstractions of tables; 5. Views can combine multiple tables in queries, and tables can only query a single table; 6. Tables are permanent structures in the database, views are not; 7. Views can create views with the same name, but tables cannot create tables with the same name, etc.
- SQL 6240 2023-09-04 15:13:10
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- Meituan interview question: Have you ever encountered slow SQL? How was it solved?
- MySQL's slow query log is a log record provided by MySQL. It is used to record statements in MySQL whose query time exceeds (greater than) the set threshold (long_query_time) and records them in the slow query log.
- SQL 1688 2023-08-24 15:41:08
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- Interviewer: Are you familiar with SQL optimization? I only know 20 kinds, but there are far more...
- Faced with this problem, don’t be afraid. Brother Tian has prepared the following 52 SQL statement performance optimization strategies for you. If it doesn't work, just memorize a few more items, and you'll still be able to deal with your immediate needs.
- SQL 1222 2023-08-17 16:36:22
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