sql-server - sql update先删除再插入吗？

Question

Sql server究竟是如何进行更新操作的？它会进行就地更新吗？或者它对受影响的每一行进行删除然后插入？我知道更新操作类似于删除然后插入，因为旧值存储在删除的中，新值存储在插入的...

有人告诉我更新操作是通过删除然后插入来完成的，但我不确定为什么要这样实现。请赐教。

Answer 1

MSDN Update section :

The Database Engine converts a partial update to a full update when the UPDATE statement causes either of these actions:

• Changes a key column of the partitioned view or table.

• Modifies more than one row and also updates the key of a nonunique clustered index to a nonconstant value.

和partial update

Partial-update transaction directly writes a character string at a user-defined position of a table column without issuing a delete and replace command, as would happen in a full update.

Partial update does not support multibyte character set conversion. Partial update support is restricted to Microsoft SQL Server.

我进行了一些搜索，看来您问题的答案取决于您要更新的内容。

希望这对您有所帮助。