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Technical Articles

Database

How to search for special characters like '%' or '_' in SQL?

To search for special characters such as % or _ in SQL, they must be escaped using ESCAPE clause or parentheses. 1. Use ESCAPE keyword to define escape characters, such as SELECT*FROMtable_nameWHEREcolumnnameLIKE'%\%%'ESCAPE'\', where \% represents the literal %; 2. Other escape characters such as!, such as LIKE'%!%%'ESCAPE'!'; 3. In SQLServer and PostgreSQL, you can enclose special characters, such as LIKE'%[%]%' or LIKE'%[]%', so that they match literally; 4. MySQL supports ESCAPE and allows customization.

Aug 11, 2025 pm 03:21 PM

Analyzing Logs and Metrics for a Healthy MongoDB Environment

Monitorkeyperformancemetricssuchasoperationlatency,queuelength,memoryusage,connectioncount,replicationlag,anddiskI/Otodetectbottlenecksandsystemstress.2.AnalyzeMongoDBlogsforslowqueries,replicationissues,storagewarnings,andauthenticationfailuresusing

Aug 11, 2025 pm 03:15 PM

How to use the CONVERT function in SQL?

The CONVERT function is used to convert the data type of an expression to another type in SQL, mainly used in SQLServer and MySQL, but the syntax is different. 1. In SQLServer, the syntax is CONVERT(data_type[(length)],expression,[style]), where data_type is the target type, length is the optional length, expression is the value to be converted, and style is the date format code; for example: CONVERT(DATETIME,'2023-10-01') converts the string to a date, CONVERT(VARCHAR(10),

Aug 11, 2025 pm 03:12 PM

How to trim leading and trailing spaces from a string in SQL?

To trim the beginning and end spaces of a string, you should use the TRIM() function; 1. Use TRIM('HelloWorld') to remove the beginning and end spaces, and the result is 'HelloWorld'; 2. If only the first space is removed, use LTRIM() for MySQL and SQLServer, and use TRIM(LEADINGFROM); If only the tail spaces are removed, use RTRIM() or TRIM(TRAILINGFROM); 3. You can also specify characters, such as TRIM(BOTH'x'FROM'xxxHelloWorldxxx') to remove the beginning and end x, and the result is 'HelloWorld'. This method is

Aug 11, 2025 pm 03:11 PM

How to split a delimited string into rows in SQL?

SQLServer uses STRING_SPLIT function to split the delimited string into rows, and the output column name is value, but the row order is not guaranteed, and additional logic needs to be maintained; 2. PostgreSQL is implemented by combining STRING_TO_ARRAY and UNNEST, and the array is naturally maintained in sequence; 3. MySQL has no built-in SPLIT function, and each element can be extracted by recursive CTE or numeric tables and SUBSTRING_INDEX; 4. Oracle uses REGEXP_SUBSTR to generate rows and divide them through regular matching; 5. SQLite has no built-in method, and elements need to be stripped one by one with recursive CTE.

Aug 11, 2025 pm 02:36 PM

How to create a stored procedure in SQL

AstoredprocedureisareusableSQLcodeblockthatcanacceptparametersandexecutecomplexlogic;2.Tocreateone,useCREATEPROCEDUREfollowedbytheprocedurename,parameters,andSQLstatementswithinaBEGIN-ENDblock;3.Syntaxvariesslightlybydatabase:SQLServerusesEXECandDECL

Aug 11, 2025 pm 02:22 PM

What are geospatial indexes, and how are they used for location-based queries?

Geospatialindexesarespecializeddatabasestructuresdesignedtoefficientlymanageandquerymulti-dimensionalspatialdata.Unlikeregularindexes,whichworkwithone-dimensionalvalueslikenamesordates,geospatialindexeshandlecomplexqueriesinvolvinggeographiclocations

Aug 11, 2025 pm 01:39 PM

Location query 地理空間索引

Implementing Row-Level Security in MySQL

MySQLdoesnothavebuilt-inrow-levelsecurity,butitcanbeimplementedusingviews,storedprocedures,andaccesscontrol.1.UseviewstofilterrowsbasedonthecurrentuserbyleveragingfunctionslikeCURRENT_USER()andamappingtabletorestrictdatavisibility.2.Restrictdirecttab

Aug 11, 2025 pm 01:33 PM

How to change a column's data type in SQL?

MySQL uses MODIFYCOLUMN, and the constraints need to be re-specified; 2. PostgreSQL uses ALTERCOLUMNTYPE, and the data is incompatible must be converted using the USING clause; 3. SQLServer uses ALTERCOLUMN, and the constraints can be modified at the same time; 4. SQLite does not support direct modification of types, and tables need to be rebuilt; data compatibility should be ensured, dependencies should be checked and data backed up before all operations to avoid problems caused by structural changes.

Aug 11, 2025 pm 01:02 PM

How to perform a search with regular expressions (regex) in SQL?

MySQL and MariaDB use REGEXP or RLIKE operators for regular matching, such as WHEREcolumn_nameREGEXP'^A'; 2. PostgreSQL uses ~ (case sensitive) and ~* (insensitive) operators to support full POSIX rules, such as WHEREcolumn_name~'^\d{3}-\d{3}-\d{4}$'; 3. Oracle and MySQL8.0 use REGEXP_LIKE functions, such as WHEREREGEXP_LIKE(column_name,'^john','i') to support flag bits; 4. SQLite does not support regular by default, and requires

Aug 11, 2025 pm 12:47 PM

How to create a view in SQL

The syntax for creating a view is the CREATEVIEWview_nameASSELECT statement; 2. The view does not store actual data, but is based on the real-time query results of the underlying table; 3. The view can be modified using CREATEORREPLACEVIEW; 4. The view can be deleted through DROPVIEW; 5. The view is suitable for simplifying complex queries, providing data access control, and maintaining interface consistency, but attention should be paid to performance and logic, and finally ends with a complete sentence.

Aug 11, 2025 pm 12:40 PM

sql view

How to compare two tables for differences in MySQL

To compare the differences between two tables in MySQL, different operations need to be performed according to the structure, data or both: 1. When comparing the table structure, use DESCRIBE or query INFORMATION_SCHEMA.COLUMNS to find columns that exist only in one table through UNIONALL and subqueries; 2. When comparing table data, use LEFTJOIN combined with ISNULL conditions to find rows that exist only in table1 or table2, and use UNIONALL to merge the results with UNIONALL; 3. When comparing rows with the same primary key but different data, use JOIN to connect the two tables and use NULL safe comparison operator to detect the difference in the values of each column; 4. You can first perform row count statistics checks and compare them through COUNT(*)

Aug 11, 2025 pm 12:14 PM

What is the 'score' in a Sorted Set?

ThescoreinaRedisSortedSetisanumericalvaluethatdeterminestheelement'spositionwithintheset.Unlikeregularsets,whichareunordered,SortedSetsusescorestomaintainanautomaticorderfromsmallesttolargest.Eachmemberisassociatedwithascore,enablingdynamicrankingand

Aug 11, 2025 am 11:55 AM

score

How to get the identity of the last inserted row in SQL?

InSQLServer,useSCOPE_IDENTITY()togetthelastinsertedidentityvaluewithinthesamescope,avoidingissueswithtriggers;2.InMySQL,useLAST_INSERT_ID()immediatelyafterINSERT,whichisconnection-specificandreliable;3.InPostgreSQL,usetheRETURNINGclauseintheINSERTsta

Aug 11, 2025 am 11:50 AM

sql Insert row