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Technical Articles

Database

SQL

Detailed explanation of usage of sql statement case when

The usage of [case when] in SQL is: 1. Use [case field name when field value then value 1 else value 2 end] to judge the field value; 2. Use [case when condition then value 1 else value 2 end] to judge Field value.

Jun 13, 2020 pm 02:54 PM

sql

MySQL modifies the table structure and its functions of adding, deleting and modifying fields

mysql is powerful, has many uses, and has many unique uses. This article introduces in detail the MySQL table structure modification and its functions of adding, deleting, and modifying fields. I hope it will help everyone.

Jun 12, 2020 am 09:00 AM

修改表结构

What is the usage of SQL Union?

Union is a SQL operator used to combine the results of multiple SELECT statements into a result set. Its syntax is "UNION ALL SELECT * FROM TableB UNION SELECT * FROM TableC".

Jun 09, 2020 pm 04:21 PM

sql union

How to use like in sql

In SQL, like uses wildcards to compare a value with similar values. Its usage is: 1. Percent wildcard character, the syntax is [WHERE SALARY LIKE '200%']; 2. Percent wildcard character, the syntax is [WHERE SALARY] LIKE '_2%3'].

Jun 09, 2020 pm 03:40 PM

sql

What is the sql statement to view the table structure?

The sql statement to view the table structure is: 1. In mysql, use the sql statement [desc table name] to view; 2. In Oracle, use the sql statement [select * from user_tab_columns where table_name=‘uppercase table name‘] to view.

Jun 08, 2020 am 11:46 AM

sql mysql oracle

How to delete data using delete statement

How to use the delete statement to delete data: first create a temporary table; then use the statement "select * from" to query the temporary table; finally use the delete statement "delete #tblDelete where Code = 'Code3'" to delete the data.

May 26, 2020 am 10:49 AM

delete

What are the command phrases used for grouping in database queries?

The command phrase that needs to be grouped in database queries is "GROUP BY". The "GROUP BY" phrase is used to group the query results and can be used for group summary. The "HAVING" phrase cannot be separated from the "GROUP BY" phrase. exist independently.

May 16, 2020 am 09:45 AM

数据库查询

What is the sql statement to delete an index?

The SQL statement to delete the index is: [drop index [indexname] on mytable;]. We can use the [alter table tbl_name add index index_name (column_list):] statement to add an index.

May 13, 2020 am 11:17 AM

索引 sql

How to install PLSQl program

How to install the PLSQl program: first download the "plsql developer" package, unzip it and enter the program directory; then select the "plsql developer" installer and right-click with the mouse; then in the installation interface, select "Agree to the installation agreement"; finally select Just install the path.

May 12, 2020 am 10:55 AM

PLSQl

How to set primary key in database

How to set the primary key of the database: first open the [SQL Server Management Studio] management tool and connect to the database; then right-click the [Table] menu and select [New] -> [Table]; finally hold down the [ctrl] key and right-click Select [Set Primary Key].

May 12, 2020 am 10:45 AM

数据库

What to do if the installation of sql server 2008 fails to restart the computer

The solution to "Failed to restart the computer" when installing SQL Server 2008: First press the key combination "Win+R" on the keyboard to bring up the run window; then open the registry management interface; finally find and delete " PendingFileRenameOperations" item is enough.

May 10, 2020 am 09:02 AM

sql server

What is the usage of exists in oracle?

Usage of exists in oracle: exists is followed by a subquery, the purpose is to check whether the result of the subquery is true. If the subquery is true, the outer sql statement is executed. exists does not return data, only true or false.

May 09, 2020 pm 01:17 PM

oracle exists

What is the full Chinese name of sql?

The full Chinese name of sql is Structured Query Language. It is a special-purpose programming language, a database query and programming language, used to access data and query, update and manage relational database systems.

May 09, 2020 am 10:44 AM

sql 中文全称