During a trigger operation, two logical tables store deleted and inserted records. The deleted and inserted logical tables cannot be referenced outside the trigger body. Therefore to be able to optimize a SQL statement used in a trigger two temporary tables are used to simulate the inserted and deleted tables.
For example:
INSERT INTO EMP_SMALL (EMP_ID,
EMP_NAME,
EMP_SALARY)
SELECT A.EMP_ID,
A.EMP_NAME,
B.EMP_SALARY
FROM EMPLOYEE A,
Inserted B
WHERE A.EMP_ID = B.EMP_ID
SELECT *
INTO #inserted_simulation_table
FROM dbo.EMPLOYEE
WHERE 1 = 2
INSERT INTO EMP_SMALL (EMP_ID,
EMP_NAME,
EMP_SALARY)
SELECT A.EMP_ID,
A.EMP_NAME,
B.EMP_SALARY
FROM EMPLOYEE A,
#inserted_simulation_table B
WHERE A.EMP_ID = B.EMP_ID
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