Created: February-09, 2022 In this tutorial, Our goal is to explore
the concept of multiple primary keys of a table in MySQL. Many-a-times, businesses, and organizations must assign certain columns as the primary key. This If more than one column has been assigned as the We will certainly get an error if we push or insert The table can have more than one To be precise, multiple
primary keys are not assigned to columns, but multiple columns can be described while stating the Before we begin, we create a dummy dataset to work with. Here we create a table, Here as we can see,
we have set the The above query creates a table with rows with first and last names. To view the entries in the data, we make use of the following code. The query mentioned above would give the following output. Now let us use the
In our case, we would need to write the following query to understand the details of the table
This statement would help us fetch the table’s intricate details like the data type associated with each column, different columns and their names, the keys associated with each column, and any extra information relevant to the table.
The table above shows that the fields One might need to do this because many a time, businesses need to maintain records such that there exist no duplicate combinations of certain columns. For example, suppose a product-based company needs to limit customer orders and the number of products associated with the customer every day. In that case, they might need to set two primary keys as customer id and product id to match the data and perform any operation necessary without any duplicate combination. Therefore, with the help of the queries above, we can efficiently set multiple primary keys to a table in MySQL. Related Article - MySQL KeySummary: in this tutorial, you will learn how to use MySQL primary key constraint to create the primary key for a table. Introduction to MySQL primary keyA primary key is a column or a set of columns that uniquely identifies each row in the table. The primary key follows these rules:
Because MySQL works faster with integers, the data type of the primary key column should be the integer e.g.,
A primary key column often has the When you define a primary key for a table, MySQL automatically creates an index called MySQL PRIMARY KEY examplesThe 1) Define a PRIMARY KEY constraint in CREATE TABLETypically, you define the primary key for a table in the If the primary key has one column, you can use the
When the primary key has more than one column, you must use the
In this syntax, you separate columns in the The
The following
example creates a table named
This statement creates the
In case the primary key consists of multiple columns, you must specify them at the end of the The following example creates the
Note that the statement also created two foreign key constraints. 2) Define PRIMARY KEY constraints using ALTER TABLEIf a table, for some reasons, does
not have a primary key, you can use the
The following example adds the First, create the
Second, add a primary key to the
If you add a primary key to a table that already has data. The data in the column(s), which will be included in the primary key, must be unique and not NULL. PRIMARY KEY vs. UNIQUE KEY vs. KEY
A Suppose that Add a
Add a
In this tutorial, you have learned how to create a primary key for a new table or add a primary key to an existing table.
Was this tutorial helpful? Can we have 2 primary keys in a table in mysql?Primary keys must contain UNIQUE values, and cannot contain NULL values. A table can have only ONE primary key; and in the table, this primary key can consist of single or multiple columns (fields).
Can you have 2 primary keys in a table?Each table can only have one primary key. Access can automatically create a primary key field for you when you create a table, or you can specify the fields that you want to use as the primary key.
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