Column constraints are the rules applied to the values of individual columns:
PRIMARY KEYconstraint can be used to uniquely identify the row.
UNIQUEcolumns have a different value for every row.
NOT NULLcolumns must have a value.
DEFAULTassigns a default value for the column when no value is specified.
There can be only one
PRIMARY KEY column per table and multiple
CREATE TABLE student ( id INTEGER PRIMARY KEY, name TEXT UNIQUE, grade INTEGER NOT NULL, age INTEGER DEFAULT 10 );
CREATE TABLE Statment
CREATE TABLE statement creates a new table in a database. It allows one to specify the name of the table and the name of each column in the table.
CREATE TABLE table_name ( column1 datatype, column2 datatype, column3 datatype );
INSERT INTO statement is used to add a new record (row) to a table.
It has two forms as shown:
- Insert into columns in order.
- Insert into columns by name.
-- Insert into columns in order: INSERT INTO table_name VALUES (value1, value2); -- Insert into columns by name: INSERT INTO table_name (column1, column2) VALUES (value1, value2);
ALTER TABLE Statement
ALTER TABLE statement is used to modify the columns of an existing table. When combined with the
ADD COLUMN clause, it is used to add a new column.
ALTER TABLE table_name ADD column_name datatype;
DELETE statement is used to delete records (rows) in a table. The
WHERE clause specifies which record or records that should be deleted. If the
WHERE clause is omitted, all records will be deleted.
DELETE FROM table_name WHERE some_column = some_value;
UPDATE statement is used to edit records (rows) in a table. It includes a
SET clause that indicates the column to edit and a
WHERE clause for specifying the record(s).
UPDATE table_name SET column1 = value1, column2 = value2 WHERE some_column = some_value;