Triggers are stored techniques that are fired when knowledge is modified in an fundamental table. They're able to Appraise info being included to the desk for validation needs, or might make improvements in that or other fields depending upon the price of that facts. You should utilize them even to execute more info a independent saved treatment, or to roll back a data modification or a complete transaction.
In before versions of SQL Server, triggers ended up utilized to take care of referential integrity. In present-day variations, constraints and overseas keys are applied to accomplish A great deal of People responsibilities, but triggers remain employed to perform a lot more complex tasks than that are available to the built-in newer resources, like complex column constraints, https://en.wikipedia.org/wiki/?search=먹튀검증 evaluation of tables in other databases, complicated defaults, or cascading routines involving multiple variations in a number of tables.
Triggers are developed in the Organization Supervisor, or during the Question Analyzer through the object browser. You will also find templates for triggers in the Query Analyzer (EditInsert Result in). Triggers could be established with the following syntax:
CREATE TRIGGER trigger_name
ON table check out
[ WITH ENCRYPTION ]
FOR Soon after In lieu of [ INSERT ] [ , ] [ UPDATE ]
[ WITH APPEND ]
[ NOT FOR REPLICATION ]
AS
[ IF UPDATE ( column )
[ AND OR UPDATE ( column ) ]
[ … n ]
IF ( COLUMNS_UPDATED ( ) bitwise_operator updated_bitmask )
comparison_operator column_bitmask [ … n ]
]
sql_statement [ … n ]
There are 2 sorts of triggers: Just after and As opposed to. Right after triggers Soon after TRIGGERS fireplace after the info is improved, either by insert, delete, or update. If the information is inappropriate, as defined during the result in, the modification can be rolled again to in which it absolutely was ahead of the data was modified. Immediately after triggers Immediately after TRIGGERS can't be placed on sights, and can't be utilized on multiple desk. Also, the textual content, ntext, and graphic columns can not be referenced in an right after set off. AFTER TRIGGERS.
After triggers Right after TRIGGERS is often nested to 32 levels deep, and will be identified as recursively, once again to 32 concentrations.
In lieu of As an alternative to triggers make the validation before the modification. Even so, In place of As an alternative to triggers CAN can be used on views. They don't let recursion, and you will only have 1 As opposed to In lieu of induce for every table. And You can not use an As opposed to As opposed to induce having a cascade.
Assets
Info on Constraints and Triggers
This resource discusses about constraints and triggers intimately.
Information and facts: Produce Induce
This resource is helpful in comprehending the workings of triggers intimately.
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