Advantages and disadvantages of SQL Server

In general, the index will speed up the query, but will affect the insertion, modification, deletion of data, and occupy the physical space;
So we should create the index reasonably, and we should create the aggregate index first, and then create the non-aggregated index.
To create an index on a column that is frequently queried, and avoid too many indexes if the table columns are small;

Advantages Detailed Description:
Creating an index can greatly improve the performance of your system.
First, by creating a unique index, you can guarantee the uniqueness of each row of data in a database table.
Second, it can greatly speed up the retrieval of data, which is the main reason for creating indexes.
Thirdly, the connection between tables and tables can be accelerated, particularly in terms of achieving referential integrity of the data.
Finally, when using grouping and sorting clauses for data retrieval, you can also significantly reduce the time to group and sort in queries.
By using the index, we can improve the performance of the system by using the optimized hidden device in the process of querying.

Disadvantages Detailed Description:
First, it takes time to create indexes and maintain indexes, and this time increases as the amount of data increases.
Second, the index needs to occupy the physical space, in addition to the data table to occupy the data space, each index also occupies a certain amount of physical space, if you want to establish a clustered index, then the space will be larger.
Thirdly, when the data in the table is added, deleted and modified, the index should be maintained dynamically, thus reducing the maintenance speed of the data.

Indexes are built on top of some columns in a database table. Therefore, when you create an index, you should carefully consider which columns you can create an index on, and on which columns you cannot create an index. In general, you should create indexes on these columns, such as: on columns that are often searched, you can speed up the search, enforce the uniqueness of the column on the column that is the primary key, and arrange the structure of the data in the organization table; These columns are mostly foreign keys, which can speed up the connection. Create an index on a column that often needs to be searched by scope, because the index is sorted, its specified range is contiguous, and the index is created on columns that are often ordered, because the index is sorted so that the query can take advantage of the sorting of the index to speed up the sort query time To speed up the judgment of a condition by creating an index on a column that is often used in the WHERE clause.

Similarly, indexes should not be created for some columns. In general, these columns that should not be indexed have the following characteristics: first, you should not create an index for columns that are seldom used or referenced in a query. This is because, since these columns are seldom used, they are indexed or non-indexed and do not improve query speed. Conversely, by increasing the index, it reduces the system maintenance speed and increases the space requirement. Second, you should not increase the index for columns that have only a few data values. This is because, because these columns have very few values, such as the gender column of the personnel table, in the results of the query, the data rows of the result set occupy a large proportion of the data rows in the table, that is, the data rows that need to be searched in the table are large. Increasing the index does not significantly speed up the retrieval. Third, for those columns defined as text, the image and bit data types should not be indexed. This is because the amount of data in these columns is either quite large or has very little value. The index should not be created when the performance of the modification is far greater than the retrieval performance. This is because modifying performance and retrieving performance are conflicting. When you increase the index, the retrieval performance is improved, but the performance of the modification is reduced. When you reduce the index, you increase the performance of the modification and reduce the retrieval performance. Therefore, the index should not be created when the performance of the modification is far greater than the retrieval performance

Advantages and disadvantages of SQL Server