A Primary Key is a special column in the relational database table that is dedicated to identifying records within a table uniquely. In other words, a single column or a set of columns that uniquely identifies each row in the table is called the Primary key or generally abbreviated as PK in the SQL.
Before you add a primary key to the database, you should add primary key constraints first. In case, there are multiple columns used as the primary key then it is named as the composite primary key but make sure that you are using a few columns only.
The Primary Key is good in both performance and storage. The more columns are you using as the primary key, more storage you needed generally. When we are talking about the performance, then less data generally leads to better performance standards.
A primary key is defined as the single column or a set of columns that uniquely identifies each row in the table. As soon as one primary key constraint is defined for the table, the database engine automatically creates a unique index for the primary key column. The biggest advantage of defining primary key is that we get faster access. This is not possible adding a primary key constraint if it contains more than 32 columns.
The primary key is taken as the critical component of an efficient relational database system. In the absence of the primary key that is closely related to the Foreign key in SQL, the relational database system would not work as usual. Almost everyone deals with the primary key in their daily life unknowingly. For example, students are given unique ID no in Schools and college, employees are given a unique ID in the offices, all US citizens have uniquely identifiable social security numbers as given by the government.
If we will take the example of a Bank then branch code or bank name is same for all users but they are given unique account number for identification. In order to identify all customers uniquely, the bank makes sure two of the users should not have the same account number. In case, values are the same then they should be eliminated quickly. As soon as some column is defined as allows secure handling of data and faster method of data access too.
For example, if you are asked to tell your surname then multiple results will be displayed but with the help of primary key only one result is returned and it makes data handling much easier than your expectations.
Primary keys are usually specified at the time of new table creation or at the time when changing the structure of the existing table using the Alter Table statement. Here, in the example below, we have given the general syntax for the primary key constraint using ‘Create Table’ and ‘Alter Table’ both. A constraint is the combination of the NOT NULL and the UNIQUE constraint. It ensures that the particular column is the combination of two or more columns in a table and have a unique identity too that helps in identifying the particular record within a table more quickly and easily.
Setting the primary keys in SQL is one of the important factors in database design because the choice of a primary key could have the significant impact on the performance, and usability of the entire database. Here, we have given the best practices to follows when setting the primary key in SQL to make sure that database lookups are speedy and reliable.
Based on the conditions as specified earlier, you should match the criteria and define the primary key accordingly. The candidate that satisfies the maximum number of conditions is taken as the primary key of a table. If you don’t find any suitable candidate then consider the surrogate key as the primary key.
A few database developers may consider these options the obvious choices for the primary key but we strongly recommend avoiding these values or they are taken as the poor choice instead, by experienced database developers.
The process of removing a primary key is pretty straightforward. If you can create the primary key then there is provision to delete it as well based on the requirements. To remove the primary key in SQL, drop keyword is used. Here, is the syntax to remove the primary key in the SQL-
As you can see that deleting a primary key in SQL is quite easier but it will remove all indexes too associated with the primary key. If the index is clustered, it means that we have a huge heap on our hands and it can affect the performance of non-clustered indexed that were pointing to the clustered indexes. Further, it will hit the performance as well based on the complexity of queries and the amount of data. So, you have to be extra careful when dropping the primary keys. You should not drop the primary key on production servers during the peak hours. With this blog, you will get a deep idea of the primary key and how to create, set, or remove the primary key in SQL. A depth understanding of the concept always helps you in a successful implementation and wondering database management too.
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