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: