How do I create a non unique index when building a database? It s best to be specific

Syntax: create [index type] index index name.

on Table Name (Column Name).

with fillfactor = fill factor value 0 100

go instance

use library name.

goif exists (select * from sysindexes where name='ix_test_tname') -- Detect if the ix test tname index already exists.

drop index is deleted if it exists.

Create an index. create nonclustered index ix test tname -- Create a nonclustered index.

on test(tname) - Creates an index for the tname field of the test table.

with fillfactor = 30 -- the fill factor is 30%.

goselect * from test(index = ix_test_tname) where tname = 'a'--Specify the query to be indexed by 'ix test tname'.

A MySQL database can create an index for a view by following the following method:

1. When creating an index for a data table in a MySQL database, you can directly create an index when creating a table, as shown in the following figure.

2. You can use the explain command to view the index being used.

3. In addition, you can also create a unique index, and the value of the constrained column is required by the unique index to be a unique value and cannot be repeated.

4. If the value of the unique index column is duplicated during creation, it cannot be inserted normally, as shown in the following figure.

5. In addition, you can also use multiidx to create compound indexes in the same table, as shown in the following figure.

6. On an existing table, you can also add an index directly through create, as shown in the following figure.

The database indexes, and if it is a one-to-one permanent relationship, it is the primary index; If it's a one-to-many relationship, it's one primary index and one normal index. The purpose of indexing is to establish relationships between tables.

You can set multiple common indexes on a table, but you can set only one primary key, which is unique.

A primary key can consist of one or more fields.

Views cannot create indexes, you can create related indexes on the tables used in the view for optimization purposes.

The view should not be indexed.

create index username. Index name on username. Table name (column name): nologging noparallel

Let's face up to your problem first.

Whether the data is duplicated or not is not an important basis for indexing, or even a basis.

As long as it's not an exact duplicate (that element is the same for all tuples), then indexing makes sense.

Even if the current data is completely duplicated, it is not impossible to build indexes, which is a bit complicated and will not be detailed.

For your later questions, I can give you a piece of advice on how to build an index, "how to look it up".

The only reason for indexing is to query (generalized query), in fact, indexing will make the space occupied by the data store larger, and sometimes the space occupied by the index will check the space of the data itself. Index creation will also make data insertion slower, and in some cases, it will be unbearable, so one of the important tasks of DBA is to check the index hierarchy and optimize it.

The only benefit of indexing is that it is faster when querying by index. Whether the two fields of type and status are suitable for indexing depends on whether you want to search according to these two fields. The order in which the searches are made determines how the index is built.

For index types and indexing methods, I recommend that.

normal

And. btree

It works in most cases. If you are involved in a big data processing project and have special requirements for data storage and retrieval, then you need to analyze multiple levels, such as data throughput, data variance, average deviation, and many other parameters before considering whether to use clustered indexes (mysql does not seem to have clustered indexes yet), as for whether it is a unique index, I recommend not using it, even if you can determine that the data is unique, do not use it, and full-text indexes are not necessary.