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This article will explain in detail the use of SQL Server database default value for you. The editor thinks it is very practical, so I share it with you for reference. I hope you can get something after reading this article.

The summary of the usage of SQLServer database defaultvalue is the main content of this article. The following editor to explain the SQLServer database defaultvalue how to use?

How to use SQLServer Database defaultvalue

1. The default value constraint added to the field when the table is created

CREATETABLE "dbo". "Test" (idintPRIMARYKEY,sexvarchar (10) DEFAULT ('boy'), namevarchar (40), ageintDEFAULT ((1)),)

Note:

At this point, the default value is the constraint, and there is no constraint name. DMBS automatically adds a "default constraint name" to it. Note how the varchar type and int type are written in DEFAULT: wrap the value value with''and (), respectively.

two。 The default value constraint added to the field after the table is created

Altertable [DBO]. [test] addconstraintTest_name_DefaultDefault ('Tom') forbaseCurrencyCode

Note:

At this point, you must write a constraint name to prevent duplicate names.

How to use SQLServer Database defaultvalue

3. Modify the original default value constraint of the field

Declare@csnamevarchar (100) set@csname=''select@csname= [name] fromsysobjectswhereid= (selectcdefaultfromsyscolumnswhereid=object_id ('Test') andname='age') exec (' alter table [DBO]. [test] dropconstraint'+@csname) exec ('alter table [DBO]. [test] addconstraint'+@csname+'Default ((18)) forage')

Note:

The default value constraint cannot be modified. When you must drop and then adddrop, you must know the name of the current default constraint. Through the sql above, you can find out the "default constraint name" bound to the age field of the Test table before you can drop.

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