We can use the ALTER TABLE statement to add the NOT NULL constraints on the columns of the existing tables as follows: ALTER TABLE tbl_name ALTER COLUMN col_name SET NOT NULL Add NOT-NULL Constraint on Columns which are Already Exist INSERT INTO products(name, price)Īs you can see, we are trying to insert a NULL value in price, which violates the constraint added on the price column, so we will get the following exception as an output.Ģ. Now, we will try to insert some NULL values in the products table using the following INSERT INTO statement. Illustrate the result of the above statement by using the following snapshot and SQL statement. We will insert some acceptable values in the products table using the INSERT INTO statement. The order of the constraint definition is not important. In PostgreSQL, we can have multiple constraints on a single like NOT NULL, FOREIGN KEY, UNIQUE, and CHECK defined one after the other. We have used the NOT NULL keyword after the data-type of the column to define the NOT NULL constraint. Consider the following CREATE TABLE statement to create a new table name products with a not-null constraint. We will create a table of name products that will have a NOT-NULL constraint added on some columns. Add NOT-NULL Constraint on Columns during Table Creation We will go through the following examples one by one to understand the PostgreSQL NOT NULL constraint in detail.ġ. In PostgreSQL, the column can have multiple constraints defined on it, which means that a column may have different constraints along with NOT NULL constraints.Įxamples to Implement NOT NULL in PostgreSQL. The NOT NULL constraint is used with the column so-termed as a column constraint, not a table constraint.
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