Hello and welcome to our comprehensive guide on how to describe a table in SQL Server. If you’re not a seasoned database administrator, this might seem daunting at first, but don’t worry – we’ve got you covered. In this article, we’ll take you through everything you need to know about describing SQL Server tables, including the syntax, the different types of descriptions, and some frequently asked questions. So, let’s dive in!
What is the SQL Server describe table command?
The describe table command is used to retrieve information about a table in a SQL Server database. This command shows the column names, their data types, any constraints on the columns, and other information about the table. In SQL Server, the command for describing a table is sp_help, which stands for stored procedure help. The syntax for the sp_help command is:
| Command | Description |
|---|---|
| sp_help [table_name] | Returns information about the specified table and its columns. |
Let’s take a closer look at the syntax and see how we can use it to describe a table in SQL Server.
The syntax of the SQL Server describe table command
The syntax for the SQL Server describe table command is simple:
| Command | Description |
|---|---|
| sp_help [table_name] | Returns information about the specified table and its columns. |
So, to describe a table in SQL Server, all you need to do is replace “[table_name]” with the name of the table you want to describe. For example:
| Command | Description |
|---|---|
| sp_help customers | Returns information about the “customers” table in the current database. |
Now that you know the syntax for the SQL Server describe table command, let’s take a closer look at the different types of descriptions you can get.
The different types of SQL Server table descriptions
When you execute the sp_help command in SQL Server, you’ll get several types of descriptions for the table you’re interested in. These include:
- Column names and data types
- Constraints on the columns
- Indexes on the table
- Foreign keys and references to other tables
- Triggers on the table
- Computed columns
- FileGroup and Partitioning schemes
Let’s take a closer look at each of these types of descriptions and see what they mean.
Column names and data types
The first type of description you’ll get when you execute the sp_help command is a list of the column names and their data types. This is the most basic information about the table, and it gives you a quick overview of what kind of data is stored in the table. For example:
| Column_name | Type | Length | Nullable |
|---|---|---|---|
| customer_id | int | 4 | no |
| customer_name | varchar | 50 | no |
| customer_email | varchar | 100 | yes |
| customer_phone | varchar | 20 | yes |
In this example, we can see that the “customers” table has four columns: customer_id, customer_name, customer_email, and customer_phone. The data types for these columns are “int”, “varchar”, and “numeric”. We can also see the length of each column and whether it allows null values.
Constraints on the columns
The next type of description you’ll get is a list of the constraints on each column in the table. Constraints are rules that are applied to the data in the column to ensure that it meets certain requirements. For example, you might have a constraint that requires a column to be unique, or that it cannot be null. Here’s an example of what the constraint information might look like in the sp_help command:
| Column_name | Type | Length | Nullable | Constraint_name | Type |
|---|---|---|---|---|---|
| customer_id | int | 4 | no | PK__customer__A4AE64B84C372E29 | PRIMARY KEY |
| customer_name | varchar | 50 | no | NULL | NULL |
| customer_email | varchar | 100 | yes | IX_customers_email | UNIQUE INDEX |
| customer_phone | varchar | 20 | yes | NULL | NULL |
In this example, we can see that there are several constraints on the columns of the “customers” table. The customer_id column has a PRIMARY KEY constraint, which means that it is a unique identifier for each row in the table. The customer_name column does not have any constraints. The customer_email column has a UNIQUE INDEX constraint, which means that no two rows in the table can have the same email address. Finally, the customer_phone column does not have any constraints.
Indexes on the table
The third type of description you’ll get is a list of the indexes on the table. Indexes are used to speed up searches on the table by creating a sort of “map” of the data. When you execute a query that includes a search for a particular value in a column, the index can be used to quickly find all the rows that match that value. Here’s an example of what the index information might look like in the sp_help command:
| Name | Description |
|---|---|
| PK__customer__A4AE64B84C372E29 | PRIMARY KEY CLUSTERED (customer_id) |
| IX_customers_email | UNIQUE NONCLUSTERED (customer_email) |
In this example, we can see that there are two indexes on the “customers” table: a primary key clustered index on the customer_id column, and a unique nonclustered index on the customer_email column. The clustered index is the most important index on the table, as it determines the physical order of the rows in the table. The nonclustered index is used to speed up searches for specific email addresses.
Foreign keys and references to other tables
The fourth type of description you’ll get is a list of any foreign keys on the table, as well as any references from other tables. A foreign key is a column in one table that refers to the primary key of another table. This is used to establish relationships between tables and ensure that data is consistent across them. Here’s an example of what the foreign key information might look like:
| Name | Description |
|---|---|
| FK_orders_customers | FOREIGN KEY (customer_id) REFERENCES customers(customer_id) |
In this example, we can see that there is a foreign key on the “orders” table that refers to the “customer_id” column in the “customers” table. This ensures that every order belongs to a valid customer.
Triggers on the table
The fifth type of description you’ll get is a list of any triggers on the table. Triggers are special stored procedures that are executed automatically when certain events occur, such as when a row is inserted, updated, or deleted. Here’s an example of what the trigger information might look like:
| Name | Description |
|---|---|
| trg_orders_insert | Executes when a new row is inserted into the “orders” table. |
| trg_orders_update | Executes when a row is updated in the “orders” table. |
| trg_orders_delete | Executes when a row is deleted from the “orders” table. |
In this example, we can see that there are three triggers on the “orders” table, one for each type of event. The trigger code might perform some additional validation or update other tables in the database.
Computed columns
The sixth type of description you’ll get is a list of any computed columns on the table. A computed column is a column whose value is calculated based on the values of other columns in the same row. Here’s an example of what the computed column information might look like:
| Column_name | Computed_expression |
|---|---|
| total_price | (price * quantity) + tax |
In this example, we can see that there is a computed column on the “orders” table called “total_price”. The value of this column is calculated based on the values of the “price”, “quantity”, and “tax” columns in the same row.
FileGroup and Partitioning schemes
The final type of description you’ll get is a list of any filegroups and partitioning schemes on the table. A filegroup is a logical container for database objects, and a partitioning scheme is a way of splitting a table into smaller, more manageable pieces. Here’s an example of what the filegroup and partitioning scheme information might look like:
| Name | Description |
|---|---|
| PRIMARY | The primary filegroup for the database. |
| orders_fg | A filegroup specifically for the “orders” table. |
| orders_part | A partitioning scheme that splits the “orders” table into four partitions based on the order date. |
In this example, we can see that there are two filegroups and one partitioning scheme in use on the “orders” table. The “PRIMARY” filegroup is the default filegroup for the database, and the “orders_fg” filegroup is used specifically for the “orders” table. The “orders_part” partitioning scheme splits the table into four partitions based on the order date, which can make it easier to manage large amounts of data.
FAQs about describing tables in SQL Server
Now that we’ve covered the basics of describing tables in SQL Server, let’s take a look at some frequently asked questions about this topic.
How can I describe all the tables in a database?
If you want to describe all the tables in a database at once, you can use the following SQL query:
| Command | Description |
|---|---|
| SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_TYPE=’BASE TABLE’ | Returns a list of all the non-system tables in the current database. |
This query will give you a list of all the non-system tables in the current database. You can then use the sp_help command to describe each table individually.
Can I use sp_help to describe a view?
No, the sp_help command cannot be used to describe a view. Views are not tables, so they don’t have the same properties as tables. To describe a view, you’ll need to use a different command, such as sp_helptext.
Is there a way to see the table description in SQL Server Management Studio?
Yes, you can see the table description in SQL Server Management Studio by right-clicking on the table in the Object Explorer and selecting “Properties”. This will bring up a dialog box with several tabs, including one called “Extended Properties”. In this tab, you can see and edit the description for the table.
How can I get more information about a column in a table?
If you want to get more information about a specific column in a table, you can use the sp_help command with the column name as a parameter. For example:
| Command | Description |
|---|---|
| sp_help customers, customer_name | Returns information about the “customer_name” column in the “customers” table. |
This command will give you detailed information about the “customer_name” column, including its data type, length, and any constraints on the column.
Can I change the table description?
Yes, you can change the table description by using the sp_addextendedproperty command. Here’s an example of how to set a new description for the “customers” table:
| Command | Description |
|---|---|
| EXEC sys.sp_addextendedproperty @name=N’MS_Description’, @value=N’This is the new description for the customers table.’, @level0type=N’Schema’,@level0name=N’dbo’, @level1type=N’Table’,@level1name=N’customers’ | Sets a new description for the “customers” table. |
Make sure that you replace the name and value parameters with the new description you want to set.
Conclusion
Describing a table in SQL Server is an important part of managing a database. By using the sp_help command, you can get a detailed view of the table’s structure, including its columns, constraints, and indexes. You can also get information about any foreign keys or triggers on the table, as well as its filegroups and partitioning schemes. If you’re new to SQL Server, this might feel overwhelming at first, but with a little practice, you’ll become more comfortable with using the sp_help command to describe tables.