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- What are the common data types in databases?
- Commonly used data types in databases are: 1. Integer data type; 2. Floating point data type, used to store decimals; 3. Binary data type; 4. Logical data type; 5. Character data type, used to store various letters , digital symbols, special symbols.
- SQL 39803 2020-06-16 17:22:16
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- Detailed explanation of sql isnull usage
- In SQL, you can use [isnull] to replace the specified replacement value with NULL. This function is used to replace a NULL value. Its syntax is [ISNULL(check_expression, replacement_value)], and its parameter 1 checks whether it is NULL.
- SQL 5834 2020-06-16 17:15:16
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- What is an inner join?
- Inner joins, the most common equivalent joins, are the earliest joins and are also called ordinary joins or natural joins. The effect is to delete all rows from the result table that do not match rows in other joined tables, so inner joins may lose information.
- SQL 9986 2020-06-16 16:44:05
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- In sql language, what is the command to delete a table?
- In SQL language, the command to delete a table is [drop], and the commands to insert, delete and query data in the table are [INSERT], [UPDATE] and [SELECT] respectively.
- SQL 9898 2020-06-16 15:09:19
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- What should I do if it prompts that restarting the computer fails when installing Server SQL2008?
- The solution to the problem of failure to restart the computer when installing Server SQL2008 is: 1. Open the Registry Editor; 2. Right-click the folder [MSSQLServer] and select [Delete]; 3. Delete the pendingFielRenameOperations option.
- SQL 8761 2020-06-16 11:35:17
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- What are the basic database operation statements?
- The basic operation statements of the database are: 1. To query the database, the statement is [SHOW DATABASES]; 2. To query the structure of the database, the statement is [CREATEDATABASE score]; 3. To create a database, the statement is [DATABASE score DEFAULT CHARSET].
- SQL 13898 2020-06-15 14:05:11
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- What is the difference between hql and sql
- The difference between hql and sql is: 1. The query is different, sql is oriented to database table query, hql is oriented to object query; 2. The judgment conditions are different, the class name followed by from in hql and the class object where are used as conditions for the object's attributes, sql What is followed by from is the table where and then the fields in the table are used to perform conditional queries.
- SQL 16011 2020-06-15 13:19:19
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- 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.
- SQL 53456 2020-06-13 15:08:27
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- 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.
- SQL 3885 2020-06-12 09:00:38
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- 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".
- SQL 9935 2020-06-09 16:21:31
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- 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'].
- SQL 20863 2020-06-09 15:40:32
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- 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.
- SQL 26428 2020-06-08 11:46:50
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- 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.
- SQL 16517 2020-05-26 10:49:07
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- 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.
- SQL 6751 2020-05-16 09:45:29
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- 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.
- SQL 10298 2020-05-13 11:17:13
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