What is the usage of IN in SQL statements?

You're not constructing the scope of in the right way. You're processing in this way as a string. And in should be followed by a range.

You can write your own function that returns the dataset to process the value into a range of in, something like this:

Hypothetical function: ft01 (nvarchar(1000)).

returns

tabletb

valint)。

So, update the in condition of the subquery in this way:

whereid

inselect

valfrom

ft01(。

Also, this workaround is only in terms of the in condition.

If the subquery has only 1 record, there is no difference between in and =, if the subquery has multiple records, using = will make an error, so in can be used no matter how many records are only queried, and = can only be used when the subquery has only 1 record.

In and exists are actually similar in understanding, but for the database, the execution order of in is to first execute only the query conditions, and then check the records with the external query to find the conditions that meet the conditions.

exists is to execute the external query first, and then execute the subquery, and after finding the external query record, it is compared with the query only that meets the criteria, if the number of entries between the external query and the subquery is very different, then the difference in efficiency is obvious.

If you don't use it like this, it's probably written incorrectly, and it should be a half-corner point".”score!

Course should be a course table that represents the database score.

I think I've just had one.

The main function of the trigger is that it cannot insert the number of the 00000001.

create

trigger

tri insert --- the name of the trigger.

onstudent-- The name of the table.

forinsert -- the insert operation.

asdeclare

student_id

char(10) – defines the variable.

select

student_id=

from-Assign a valid id to a variable.

student

sinner

joininsertedion

ifstudent_id='0000000001'--if id=''0000000001''

beginraiserror('You can't insert a student number of 1! ',16,8)--Prompt: 1 cannot be inserted.

rollback

tran -- statement sent back.

Do not perform the insertion operation. endgo

The different IDs in in are in(1@,2@) separated by commas, and if i is a character, each ID should be put in single quotation marks.

The usage of the sql in statement specifically refers to the inStructured query languageLike thisProgramming languagesSome of the statements related to in are used in it, and then the main thing in it is to use a process like querying and matching multiple fields.

For example, select in can query and match a single field with a keyword, and then use a related paragraph ** to achieve such a process, and then select in keyword can also query and match multiple fields.

And in such an SQL statement, it is usually necessary to match the different syntax of each skin punch code, and then it can realize the different processes of each judgment group. For example, changing the name of the retrieved table or the name of the column can achieve a different process, so this is a meaning of which sentence in the SQL statement is burned.

sql in syntax:

The in operator allows us to specify multiple values in a where clause.

sql in syntax:

select column_name(s)

from table_name

where column_name in (value1,value2,..

Structured Query Language (SQL), or SQL for short, is a special-purpose programming language that is a database query and programming language used to access data and query, update, and manage relational database systems.

Structured Query Language is a high-level, non-procedural programming language that allows users to work on high-level data structures. It does not require the user to specify the storage method of the data, nor does it require the user to understand the specific data storage method, so different database systems with completely different underlying structures can use the same structured query language as the interface for data input and management.

Structured Query Language (TLING) statements can be nested, which makes it extremely flexible and powerful. Open oranges.

In what is the scope of what is the attack?

on is mainly used to join two tables.

Such as: Shi Yinmin.

fromcustomersjoinorderson<2002-05-09