Shulou(Shulou.com)06/02 Report--

What to do when cross the line appears in SQL SERVER? for this question, this article introduces the corresponding analysis and solution in detail, hoping to help more partners who want to solve this problem to find a more simple and feasible way.

SQL SERVER has always appeared as a "sheep" in the database, which is not as noble as ORACLE, not as sharp as POSTGRESQL, and not as popular as MYSQL. But many people's first enlightened database is SQL SERVER. SQL SERVER uses a wide area, but with such a good-natured database, if you cross the line, don't blame him for giving you a "stomach".

Let's take a look at the following example and then talk about how it offended the "little sheep."

First of all, we don't care about the table structure of this table. The main thing is that id is the primary key.

Then the query plan of our above picture is very normal, take the main key.

The crux of the question is why a simple primary key query turns into a full table scan.

Implicit conversion in SQL Server

(there is nothing special about the table, except that it uses char as the primary key.)

Let's talk about the problem of hermit conversion. First of all, it is clear that there are two aspects of hermit conversion.

1 the given value has no type, you want SQL SERVER to guess for you, and then guess wrong

2 given the type, but no, it is not the field type that you correspond to the table, it belongs to the case where the X lip is not opposite to the X mouth.

The final result of these two cases, continue to use the above example, that is, a good = becomes >

Here is a table that can FROM TO the type (or guess) to an explicit tabular SHOW.

Of course, if there is a voice saying, how do I know if there is a hermit conversion or a lot of stored procedures in the program they write, how do I know the hermit conversion? is there any way to find out these "harmful spirits"? Of course, there is a way, directly open your extent event plan_affecting_convert, you can open the demon mirror, catch them one by one.

So when we operate the database, no matter what type of field you define, declare, or in the program, you'd better "match" him, otherwise the horns of "Little Sheep" will not feel good.

This is the answer to the question about what to do with cross the line in SQL SERVER. I hope the above content can be of some help to you. If you still have a lot of doubts to be solved, you can follow the industry information channel to learn more about it.

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