In database design, use the CREATETABLE statement to define table structures and constraints to ensure data integrity. 1. Each table needs to specify the field, data type and primary key, such as user_idINTPRIMARYKEY; 2. Add NOTNULL, UNIQUE, DEFAULT and other constraints to improve data consistency, such as emailVARCHAR(255)NOTNULLUNIQUE; 3. Use FOREIGNKEY to establish the relationship between tables, such as orders table references the primary key of the users table through user_id.

The main difference between WHERE and HAVING is the filtering timing: 1. WHERE filters rows before grouping, acting on the original data, and cannot use the aggregate function; 2. HAVING filters the results after grouping, and acting on the aggregated data, and can use the aggregate function. For example, when using WHERE to screen high-paying employees in the query, then group statistics, and then use HAVING to screen departments with an average salary of more than 60,000, the order of the two cannot be changed. WHERE always executes first to ensure that only rows that meet the conditions participate in the grouping, and HAVING further filters the final output based on the grouping results.

SQLfunctionsandstoredproceduresdifferinpurpose,returnbehavior,callingcontext,andsecurity.1.Functionsreturnasinglevalueortableandareusedforcomputationswithinqueries,whileproceduresperformcomplexoperationsanddatamodifications.2.Functionsmustreturnavalu

LAG and LEAD in SQL are window functions used to compare the current row with the previous row data. 1. LAG (column, offset, default) is used to obtain the data of the offset line before the current line. The default value is 1. If there is no previous line, the default is returned; 2. LEAD (column, offset, default) is used to obtain the subsequent line. They are often used in time series analysis, such as calculating sales changes, user behavior intervals, etc. For example, obtain the sales of the previous day through LAG (sales, 1, 0) and calculate the difference and growth rate; obtain the next visit time through LEAD (visit_date) and calculate the number of days between them in combination with DATEDIFF;

To find columns with specific names in SQL databases, it can be achieved through system information schema or the database comes with its own metadata table. 1. Use INFORMATION_SCHEMA.COLUMNS query is suitable for most SQL databases, such as MySQL, PostgreSQL and SQLServer, and matches through SELECTTABLE_NAME, COLUMN_NAME and combined with WHERECOLUMN_NAMELIKE or =; 2. Specific databases can query system tables or views, such as SQLServer uses sys.columns to combine sys.tables for JOIN query, PostgreSQL can be used through inf

Pattern matching functions in SQL include LIKE operator and REGEXP regular expression matching. 1. The LIKE operator uses wildcards '%' and '_' to perform pattern matching at basic and specific locations. 2.REGEXP is used for more complex string matching, such as the extraction of email formats and log error messages. Pattern matching is very useful in data analysis and processing, but attention should be paid to query performance issues.

Backing up and restoring SQL databases is a key operation to prevent data loss and system failure. 1. Use SSMS to visually back up the database, select complete and differential backup types and set a secure path; 2. Use T-SQL commands to achieve flexible backups, supporting automation and remote execution; 3. Recovering the database can be completed through SSMS or RESTOREDATABASE commands, and use WITHREPLACE and SINGLE_USER modes if necessary; 4. Pay attention to permission configuration, path access, avoid overwriting the production environment and verifying backup integrity. Mastering these methods can effectively ensure data security and business continuity.

Create a user using the CREATEUSER command, for example, MySQL: CREATEUSER'new_user'@'host'IDENTIFIEDBY'password'; PostgreSQL: CREATEUSERnew_userWITHPASSWORD'password'; 2. Grant permission to use the GRANT command, such as GRANTSELECTONdatabase_name.TO'new_user'@'host'; 3. Revoke permission to use the REVOKE command, such as REVOKEDELETEONdatabase_name.FROM'new_user