![]() In the above example, we have used the NOT NULL keywords after the data type of the Item_id and Quantity columns to represent the NOT NULL constraints. On executing the above command, we will get the following message: The Bills table has been created successfully into the Jtp database. Quantity NUMERIC NOT NULL CHECK(Quantity > 0),Īctual_price NUMERIC CHECK(Actual_price > 0) ![]() In the below illustration, we will use the NOT NULL constraint to check either a column can accept NULL values or not: ![]() The Syntax for PostgreSQL not-null constraint We can place the not-null constraint directly after the datatype of a column. In other words, we can say that the PostgreSQL not-null constraint is used to make sure that a column cannot have any null value.Īnd it is a column constraint which cannot be used as a table constraint that means no name can be specified to create a not-null constraint. The not null constraint is always created as a column constraint, and it represents unknown data, but it doesn't mean that the data should be null. If we don't want a column to have a NULL value, we need to explain such constraint on this column state, and NULL is now not acceptable for that particular column. In PostgreSQL, the not-null constraint is a column, which can hold the Null values by default. We should never use (=) equal operatorfor comparing the value with NULL as it always returns NULL.The IS NOT NULLoperator contradicts the output of the IS NULL.The NULL is very important as it does not equivalent to anything, even itself, as we can observe in the below expression: In such a case, the NULL specifies that the mobile number is unknown at the time of recording. But if we don't know whether the customer has a mobile number or not, we can insert NULL into the mobile number column. And it is not similar to an empty string or the number zero in the database theory.įor example, if we want to insert the customer's mobile number into a particular table, we can request his/her mobile number. The NULL is used to signifies the unknown or information missing. In this section, we are going to understand the working of the PostgreSQL NOT NULL constraint, which is used to make sure that the values of a column are not null.Įxamples of the PostgreSQL NOT NULL constraint, how to declare the PostgreSQL NOT NULL constraint, and adding NOT NULL Constraint to existing columns.īefore understanding the concept of PostgreSQL NOT NULL constraint, we are going to learn about the Null. Next → ← prev PostgreSQL Not-Null Constraint
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