find unique values

Key differs from primary keyKey is usually the index synonym. If the keyword attribute primary key is given in the column definition, then primary key can also be specified as key only. The purpose of this is to be compatible with other database

Filtering unique values and deleting duplicate values are two closely related tasks because the results shown are the same: a list of unique values. But they are still very different: when you filter a unique value, you temporarily hide the

clustered index, nonclustered index, nonclustered unique indexWe all know that establishing an appropriate index can improve query speed and optimize queries. First, whether a clustered or nonclustered index is a B-tree structure . The

clustered index, nonclustered index, nonclustered unique indexWe all know that establishing an appropriate index can improve query speed and optimize queries. First, whether a clustered or nonclustered index is a B-tree structure . The

Index type1. Unique index: Unique index does not allow two rows to have the same index value2. Primary KEY index: Defining a primary key for a table will automatically create a primary key index, which is a special type of unique index. The primary

Today, I was asked a question. I think it is quite interesting. now I will record it and discuss it with you. The problem is: in a table, there is a field that can be blank. null can be repeated, but the value that is not empty must be unique. Today,

Clustered index, nonclustered index, nonclustered unique indexWe all know that establishing an appropriate index can improve query speed and optimize queries. First, whether a clustered or nonclustered index is a B-tree structure . The

Today, my classmate asked me a question, I think it is very interesting, now recorded down to discuss. The problem is: in a table, there is a field that is allowed to be empty, and null can be repeated, but a value that is not NULL needs to be

The following code creates a table structure: Copy codeThe Code is as follows: create table test_tb ( TestId int not null identity (1, 1) primary key, Caption nvarchar (100) null ); GO Solution 1:For this question, the first thought may be: Can I

The table structure is created like the following code Copy Code code as follows: CREATE TABLE TEST_TB ( TestID int NOT null identity (1,1) primary key, Caption nvarchar (MB) null ); Go Solution 1: The first idea