Oracle CREATE Table (DDL Commands) | Oracle SQL fundamentals
You can use the CREATE TABLE statement to enforce several different kinds of #constraints on a #table: candidate keys, primary keys, foreign keys, and check conditions. A CONSTRAINT clause can constrain a single column or group of columns in a table.
The point of these constraints is to get #Oracle to do most of the work in maintaining the integrity of your #database. The more constraints you add to a table definition, the less work you have to do in applications to maintain the data. On the other hand, the more constraints there are in a table, the longer it takes to update the data.
You can specify constraints in one of two ways: as part of the column definition (known as a #column constraint) or at the end of the CREATE TABLE statement (known as a table constraint). #Clauses that constrain several columns must be table constraints.
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