Article directory The following two tables are explainedSELECTDISTINCTWHEREAND ORINBETWEENwildcardLIkeORDER BYfunctioncity tableString functionsCommonly used function examples:concatsubstrtrimregionreplacegroup byhaving Aliassubqueryexiststable linkUse subqueries to implement multi-table queriescreate viewunion intersection valueNo intersection valuecaseThe difference between null and no value (... »
1. Download mysql8.0.26 (currently the latest version) https://dev.mysql.com/downloads/mysql/ 2. No login, just download 3. Unzip the compressed package to the directory where you usually install the software. 4. Configure environment variables after decompression [This computer]-[Right-click]-[Properties]-[Advanced system settings]-[Environment variables]-[Find the path in the system variables]-[... »
Article directory Table of contents Preface 1. Three methods to start the SQL server service 1. Impact of not starting the SQL server service 2. Method 1: Use cmd to start the SQL server service 3. Method 2: Use SQL Server Configuration Manager to start the SQL server service 4. Method 3: Start the SQL server service in the service manager 2. Method of establishing database 3. Method of creating t... »
java connect to database step 1. Load the database Class.forName("com.mysql.jdbc.Driver"); 2. Link to database public static final String url="jdbc:mysql://localhost:3306/Product?userUnicode=true&characterEncoding=utf8&useSSL=false"; public static final String user ="root"; public static final String password="root"; Connection conn = DriverManager.getConnection(url, user, password); 3. ... »
1. Background insert into cm.f_l_c_eutrancelltdd_history select * from cm.f_l_c_eutrancelltdd_history@gsyd where start_time>=trunc(sysdate); Error table is locked when synchronizing data 2. Verification process 2.1 First check whether the table is locked: -- View all locked tables select b.owner TABLEOWNER, b.object_name TABLENAME, c.OSUSER LOCKBY, c.USERNAME LOGINID, c.sid SID, c.SERIAL# SERIA... »
–Five constraints–not nullnot null–primary key–unique–check check–defaultdefault–The primary key automatically increments identity table constraintsPrimary key constraints: the value cannot be null and cannot be repeatedNon-null constraint: cannot be nullDefault constraints: Default is xxCheck check constraint: judgment (male and female)Unique constraint: ... »
Uninstallation of database sql server and “SQL Server 2019 cannot download the required files. This may indicate that the version of the installer is no longer supported.” Installation issues Introducing the problem: Cleaning up the C drive caused the following problems, so I uninstalled and reinstalled and encountered the following problems. uninstall: Regarding complete uninstallatio... »
Encountered this error? Don’t know what to do? Going to cry? ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '("123456") where user='root'' at line 1 The SQL command of MySQL grant has actually been deprecated after 5.X First, check your MySQL version. Most MySQL versions that report e... »
Python crawls station B’s attention list 1. Database design and operation1. Data analysis2. Database design3. Database operations 2. Reptiles3. Complete code4. [Project Warehouse](https://github.com/Concyclics/BiliBiliFollowSpider) 1. Database design and operation 1. Data analysis Station B’s watch list is at https://api.bilibili.com/x/relation/followings?vmid=UID&pn=1&ps=50&order=desc... »
SELECT object_name(dt.object_id) Table name,si.nameIndex name,dt.avg_fragmentation_in_percent ASExternal fragmentation,dt.avg_page_space_used_in_percent ASinternal debris FROM ( SELECT object_id,index_id,avg_fragmentation_in_percent,avg_page_space_used_in_percent FROM sys.dm_db_index_physical_stats( db_id(‘PMDB2021′),null,null,null,’DETAILED’ ) WHERE ... »
