Default values

The default values for columns is valuable because it enforces data integrity and ensures that a value is entered on the database. It also means that some SQL statements are smaller than others. A standard type of statement without its column being added is an id field, where the primary key is defined, and when an INSERT statement is used, the id field is not required, as shown in the following.

The DBA can create columns to store current_timestamp in the database automatically, which is good for logging and time stamping.

sqlite> INSERT into salary (name, salary, bonus) values ('John Smith',15000,2000); sqlite> SELECT * FROM salary;

id            name         salary    bonus
-----       --------     ---------  --------
1           Peter Jones   10000      3000
2           Sam Smith     15000      1000
3           John Smith    15000      2000

Constraint checking

To ensure that the right data is inputted into columns on a table, certain rules are imposed, and these are...