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LOGICAL OPERATORS
Logical operators are used to combine multiple conditions in a query. These operators allow

you to create complex queries. They include the following types:

Operator Description

AND Returns TRUE if both conditions are true.

OR Returns TRUE if at least one condition is true.
Reverses the logical state of its operand,
NOT returning TRUE if the condition is FALSE and
vice versa.

SPECIAL OPERATORS

Some special operators in SQL are as follows:

Operator Description

Returns TRUE if all of the subquery values meet
ALL
the condition.
Returns TRUE if any of the subquery values meet
ANY
the condition.

Used to indicate a range which otherwise is
BETWEEN
done using relational operators.
Returns TRUE if the subquery returns one or
EXISTS
more records.

SQL CONSTRAINTS

SQL constraints are used to define rules for table data. These rules control the data that
can be stored in a column. Constraints are used to restrict the types of data that can be entered
into a table.

Some different types of constraints include:

NULL constraint: The NULL constraint allows a column to store NULL values. If no value is
provided during insert or update, it does not cause an error.
NOT NULL constraint: The NOT NULL constraint specifies that a column must have a value.
Records cannot be inserted or updated without providing a value for this column.

PRIMARY KEY constraint: The Primary key constraint uniquely identifies each record in a table.
Primary keys must be unique, cannot be NULL and only one primary key can exists per table.

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