如何为Oracle表添加主键（oracle添加主键）
“How to add primary key for Oracle tables”
When we create tables in Oracle, it is a good idea to set a primary key to the table as it will help maintain the integrity of the data in the table. A primary key is a column or set of columns in the table that uniquely identifies each row in that table. This ensures that the table can be uniquely identified and no duplicate records can be added.
In this article, we will discuss the different steps to create a primary key for Oracle tables.
First of all, we need to create a primary key constraint on the table by using the following statement.
`ALTER TABLE table_name ADD CONSTRAINT constraint_name PRIMARY KEY (column1, column2…);`
The constraint_name parameter is the name of the primary key constraint. The columns mentioned in the parentheses list are the columns used to create the primary key.
Once the primary key has been created, it can be used in various operations like adding a Foreign Key constraints, querying, deleting, and updating records of the table.
To delete the primary key of a table, use the following statement:
`ALTER TABLE table_name DROP PRIMARY KEY;`
To check if a primary key is present in the table, use the query below:
`SELECT column_name, constraint_name, table_name FROM USER_CONSTRAINTS WHERE CONSTRAINT_TYPE = ‘P’;`
This query will return all the columns, primary key constraints and table name where the CONSTRAINT_TYPE is set to ‘P’.
Now that we have learned how to add and delete a primary key, let us look at an example of how to add a primary key to an Oracle table.
Assuming that we have a table called ‘Customer_Order’ with the three columns ‘CustomerID’, ‘ProductID’ and ‘OrderID’, we can add a primary key as follows:
`ALTER TABLE Customer_Order ADD CONSTRAINT PK_CustomerOrder PRIMARY KEY (CustomerID, ProductID);`
This statement will create a primary key constraint ‘PK_CustomerOrder’ on the Customer_Order table.
In conclusion, we discussed the multiple steps involved in adding a primary key or deleting a primary key from Oracle tables. We also looked at an example which shows the usage of the ALTER TABLE statement to add a primary key to the Customer_Order table. Therefore, we can conclude that adding a primary key is an easy task and can be done with just a few lines of code.
