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It is a common misconception that an identity column will enforce uniqueness; however, this is not the case. If you want to enforce uniqueness on the column you must include the appropriate constraint too. In Microsoft SQL Server you have options for both the seed (starting value) and the increment. By default the seed and increment are both 1.
Sometimes databases also support alternative syntax for this; for example, MySQL allows omitting the DEFAULT keyword, and T-SQL can use DEFAULT VALUES instead of VALUES(DEFAULT). The DEFAULT keyword can also be used in normal insertion to explicitly fill a column using that column's default value:
The default start+increment form with the start value of 1 and increment of 1 is not suitable for all circumstances. There are reasons to choose each form, and trade-offs in doing so. [2] The default start and increment values might reveal information about a table that it is desired not to reveal to people viewing individual table rows.
Before Alter; After Alter; Before Drop; After Drop; Before Insert; The four main types of triggers are: Row-level trigger: This gets executed before or after any column value of a row changes. Column-level trigger: This gets executed before or after the specified column changes.
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The ALTER statement modifies an existing database object. An ALTER statement in SQL changes the properties of an object inside of a relational database management system (RDBMS). The types of objects that can be altered depends on which RDBMS is being used. The typical usage is: ALTER objecttype objectname parameters.