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 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 table_nameVALUES (value1, value2);-- Insert into columns by name:INSERT INTO table_name (column1, column2)VALUES (value1, value2);
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_nameADD 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_nameWHERE 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_nameSET column1 = value1, column2 = value2WHERE some_column = some_value;