SET IDENTITY_INSERT (Transact-SQL) allows explicit values to be inserted into the table's identity column

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Identity_insert allows you to manually insert an explicit value into the identity column of the table, onallows, off does not allow

When inserting data, the self-growing column is automatically processed by the system and does not require you to specify a value. The self-growing column allows you to specify a value only when the data is inserted when IDENTITY_INSERT is on

At any time, the Identity_insert property of only one table in a session can be set to ON. If a table has set this property to ON, when a set IDENTITY_INSERT ON statement is issued against another table, SQL Server returns an error message stating that set IDENTITY_INSERT is set to on and that its properties are reported The table that is set to ON.

The Identity_insert of table ' XXX.DBO.AAA ' is already on. Cannot perform SET operation for table ' BBB '.

You can set the previous table to off, and then open the table you want to modify to ON,

SET Identity_insertXxx onGOINSERT  intoXXX (ID)SELECTId fromAAAGOSET Identity_insertXxxoffGO----------------------------------------SET Identity_insertYYY onGOINSERT  intoYYY (ID)SELECTId fromAAAGOSET Identity_insertYYYoffGO

If the insertion value is greater than the current identity value of the table, SQL Server automatically uses the newly inserted value as the current identity value.

Set IDENTITY_INSERT settings are set at run time, not at parse time.

SET IDENTITY_INSERT table name on
SET IDENTITY_INSERT table name off

Summarize:
1. At any point in each connection session, only one table can be set IDENTITY_INSERT on, and the setting is only valid for the current session;
2. In the insert operation on the identity column, be sure to list this identity column.

SET IDENTITY_INSERT (Transact-SQL) allows explicit values to be inserted into the table's identity column