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) corresponding to the page number is also larger. If the phonetic "ha" corresponding to the word (Word) page number is more than the phonetic "ba" corresponding to the word (Word) page number. Nonclustered indexes (non-clustered) If it is not a clustered index, the physical order of the rows in the table does not match the logical order of the key values. Clustered indexes have faster data access speeds than nonclustered indexes (nonclustered index)
@elapsedSecond--(1 row (s) affected)--Find data consumption microseconds when indexing the second column--0--(s) affected)--Find the second column of data consumption microseconds after indexing the second column--0As you can see from the execution results, it is very fast to query the second column after the index is indexed.SummarizeIn general, for a table T, a federated primary key (A, a, a, b),
Is Order by sorted by a primary key not specified in SQL? sqlorder
If Order by is not specified in SQL, is the sorting based on the primary key? The answer is not necessarily. For example:
Queries the AttendanceEmpRank table. Th
Recently, you need to remove the primary key from a table in the ACCESS database in the program and then perform some operations. Then add the primary key. You can use this SQL statement to complete
Remove primary
A problem found during development last week ~~ When nhib.pdf is used, the problem of multiple constraints in a table is stuck for one day, which may be due to poor foundation ~ I am not familiar with the use of the joint primary key and nhib.pdf. It took a day and wasted a day.
It is very complicated to use the Union primary
Explore how SQL uses INFORMATION_SCHEMA system view to obtain the table's primary and foreign key information bitsCN.com 《
Parsing SQL table structure information query includes primary and foreign keys, auto-incrementThe INFORMATION_SCHEMA view is mentioned in this article.
The role of the primary key: 1) To ensure the integrity of the entity; 2) speed up the operation of the database 3) when you add a new record to a table, the database automatically checks the primary key value of the new record and does not allow the value to repeat with the primar
is to obtain a self-growing value before inserting a record operation, in the execution Insert SQL You must specify a primary key value for the record you want to insert, so you want to before "The time to get the self-increment sequence, and then use Selectkey into the input parameter map. Assuming the self-growth or IDInsertID= "Insert"Usegeneratedkeys= "true"
Use after an SQL statementSCOPE_IDENTITY ()Of course, you can also use SELECT @ IDENTITYHowever, the use of SELECT @ IDENTITY is globally up-to-date. incorrect values may be obtained.Example:Copy codeThe Code is as follows:Insert into dbo. SNS_BlogData (userName) values ('jiangyun ');SELECT SCOPE_IDENTITY ()Gets the primary key return value for the insert into op
Use after an SQL statement
SCOPE_IDENTITY ()
Of course, you can also use SELECT @ IDENTITY
However, the use of SELECT @ IDENTITY is globally up-to-date. incorrect values may be obtained.
Example:Copy codeThe Code is as follows: insert into dbo. SNS_BlogData (userName) values ('jiangyun ');SELECT SCOPE_IDENTITY ()
Gets the primary key return value for the insert
Original: Deletes all indexes of the specified table, including primary key indexes, unique indexes, and normal indexes, for SQL Server 2005.Deletes all indexes of the specified table, including primary key indexes, unique indexes, and normal indexes, for
Many people may confuse PrimaryKey with clustered index, or think this is the same thing. This concept is very incorrect. A primary key is a constraint attached to an index. This index can be a clustered index or a non-clustered index. So on one (or a group) Field
Many people may confuse Primary Key with clustered ind
Many people may confuse PrimaryKey with clustered index, or think this is the same thing. This concept is very incorrect. A primary key is a constraint attached to an index. This index can be a clustered index or a non-clustered index. So on one (or a group) Field
Many people may confuse Primary Key with clustered inde
SQL Multiple primary key tables, when the inserted data is duplicated, are prompted to violate the primary KEY constraint that cannot be inserted by the error. So, how do I find duplicate values for the inserted data? Workaround: Use Group bySuppose there is a table #a , t
= male) Five. Set the CHECK constraint. Check Age int check (age between), Six. Auto-grow. Auto_increment to be used on the primary key: Create TABLE box (ID int auto_increment primary key) Seven. Foreign key foreign key -
Label:The last day of 2014, today when importing data to the database, there is a problem, is the joint primary key to go heavy.The thing is, there is a table m, I want to find a table that imports a lot of data, and I need to set the fields a (int) and B (int) union as the primary key.But when I set the primary
Label:first, Getting started with SQL statements1. SQL statements are statements that are specific to the DBMS "talk", and the SQL syntax is recognized by different DBMS.2. The string in the SQL statement is enclosed in single quotation marks.3. SQL statements are insensitiv
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