Ricardo, I thought of using an explicit null and David confirmed that to be the solution. When altering a table an setting a default value only new rows will receive the new default value. If no default value is declared explicitly, the default value is the null value. We start by creating a test table in PostgreSQL 10: In a table definition, default values are listed after the column data type. The BOOLEAN can be abbreviated as BOOL.. We can store the data temporarily in the variable during the function execution. For example: CREATE TABLE products ( product_no integer, name text, price numeric DEFAULT 9.99); > Other option is. Up to PostgreSQL 10 when you add a column to table which has a non null default value the whole table needed to be rewritten. > You have to delete the column "next_contact" in your INSERT clause. The default default value for any new table column is the default value of the data type.. And the default default value for data types is NULL - which is the case for all basic data types in Postgres. > Do you put explicit "NULL" in the column value? Else > Null value will be inserted. a INTEGER NOT NULL DEFAULT 0, b DATETIME NOT NULL DEFAULT now()); INSERT INTO foo (a) VALUES (123); What happens here? By default, it accepts the NULL value if we do not define the NOT NULL or NULL; Adding a PostgreSQL NOT NULL Constraint to existing columns using an ALTER TABLE command. Once a table is created you can alter its configuration and set default values for a column. In PostgreSQL, we can add the NOT NULL Constraint to a column of an existing table with the ALTER TABLE command's help. In standard SQL, a Boolean value can be TRUE, FALSE, or NULL.However, PostgreSQL is quite flexible when dealing with TRUE and FALSE values. The manual on CREATE TYPE:. > So, if the column has a default value, this value Will be inserted. Below is the general syntax. ALTER TABLE ONLY users ALTER COLUMN lang SET DEFAULT 'en_GB'; To remove the default value you can use a similar SQL statement. PostgreSQL supports a single Boolean data type: BOOLEAN that can have three values: true, false and NULL.. PostgreSQL uses one byte for storing a boolean value in the database. We can modify the value stored within the variable by using the function or code block. If no default value is declared explicitly, the default value is the null value. For example: INSERT INTO contacts (contact_id, last_name, first_name, country) DEFAULT VALUES; This PostgreSQL INSERT statement would result in one record being inserted into the contacts table. This usually makes sense because a null value can be considered to represent unknown data. Well, a row is inserted into table ``foo'' where ``a'' has the value 123 and b holds the date & time of when the create DDL statement was executed. With PostgreSQL 11 this is not anymore the case and adding a column in such a way is almost instant. In PostgreSQL, you can also insert a record into a table using the DEFAULT VALUES syntax. (Details about data manipulation commands are in Chapter 6.) A data manipulation command can also request explicitly that a column be set to its default value, without having to know what that value is. * If values_rte is non-NULL (i.e., we are doing a multi-row INSERT using * values from a VALUES RTE), we populate *unused_values_attrnos with the * attribute numbers of any unused columns from the VALUES RTE. You are correct that you need a trigger, because setting a default value for the column won't work for you - default values only work for null values and don't help you in preventing blank values. The PostgreSQL variables are initialized to the NULL value if they are not defined with DEFAULT value. Lets check. But any valid value is allowed for custom types or domains. 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