sql insert unique

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

Text: "Translated" SQL Server Introduction stage eighth: Unique indexIndex design is a relatively important part of database design, the performance of the database is a crucial role, but the design of the index is not so easy things, performance is

I used to want to know what the difference was, but it was forgotten because we seldom used a unique key constraint. It was not until a few days ago that my colleague gave me a script to constrain the uniqueness of a field with a unique key

Generally, we can see that the terms "Index" and "key" are used for exchange, but they are actually different. An index is a physical structure stored in a database. A key is purely a logical concept. The key represents the integrity constraints

One, background Before using SQL Server for table partitioning, there were a lot of questions about unique indexes: Step8:sql Server When table partitions encounter a unique constraint, I did not think that in the MySQL partition will encounter the

The unique index is essentially no different from other indexes. The only difference is that the unique index does not allow the same value in the index key. Because each entry in the index corresponds to the row in the table. The unique index is

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

Unique indexIf the primary key is not set to a clustered index when it is created, it must be a unique nonclustered index. In fact, the unique index, the name Incredibles, is that it requires the value on that column to be unique. A unique index

CREATE TABLE StatementThe CREATE TABLE statement is used for creating tables in the database.SQL CREATE TABLE SyntaxCREATE table table name (column name 1 data type, column name 2 data type, column name 3 data type,....)The data type (DATA_TYPE)