sql keywords

Null value

An attribute value that has never been supplied. Such values are ambiguous and can mean that (a) the value is unknown, (b) the value is not appropriate, or (c) the value is known to be blank.

NULL constraint

In SQL, a constraint that specifies that a column may have empty cells in some or all rows.

NOT NULL constraint

In SQL, a constraint that specifies that a column must contain a value in every row

SQL TRUNCATE TABLE statement

It is used to remove all data from a table, while leaving the table structure itself in the database

SQL ALTER TABLE statement

The SQL command used to change the structure of a database table

SQL CREATE VIEW statement

The SQL command used to create a database view

SQL ADD clause

The following statement will add a column

SQL MERGE statement

This SQL command is essentially a combination of the SQL INSERT and SQL UPDATE statements, where an INSERT to UPDATE is performed depending upon existing data.

Null status

Whether the column has a NULL constraint or a NOT NULL constraint.

SQL DROP COLUMN clause

You can drop an existing column

index

is a special data structure that is created to improve database performance

SQL INSERT statement

is used to add rows of data to a table

SQL UPDATE statement

is used to change values of existing rows

SQL DROP CONSTRAINT clause

to DROP a constraint:

SQL ADD CONSTRAINT clause

to add a constraint

SQL CREATE INDEX statement

to create indexes,

SQL ALTER INDEX statement

to modify existing database indexes

SQL DROP INDEX statement

to remove indexes for the database

SQL DELETE statement

will delete the row

SQL DROP TABLE statement

will drop the TRANS table and all of its data: