2.6f

Operators and Operands

• Operands: The values upon which operators perform calculations. Can be numeric, character, or other data types.

• Operators: Symbols that specify the type of calculation to be performed.

  • Arithmetic Operators: Compute numeric values from numeric operands.

  • Logical Operators: Compute logical values from logical operands.

    • Unary Operator: Operates on one operand (e.g., NOT).

    • Binary Operator: Operates on two operands; most operators are binary.

    • NULL Behavior: Operators may return NULL when either operand is NULL.

Expression Evaluation

• An expression computes a single value based on operators and operands.

• Operator Precedence: Refers to the order in which operators in an expression are evaluated.

• Expressions may also evaluate to NULL, indicating an unassigned value.

  • Example: For instance, evaluating columns such as 'Platinum' AND 'Quality Unit Price' may involve numeric values and result in NULL if conditions aren't met.

SELECT Statement Structure

• SELECT Clause: Specifies the columns to retrieve from a data source.

  • Example: SELECT column_name, ... retrieves the specified columns.

• FROM Clause: Indicates the table from which to select rows.

  • Example: FROM table_name specifies the source table.

• Limit Clause: Can restrict the number of rows returned.

  • Example: LIMIT 100 indicates that only 100 rows should be returned.

WHERE Clause Evaluation

• WHERE Clause: Optional clause that specifies conditions for row selection.

  • A row is included if the WHERE condition evaluates to TRUE for the row's values.

  • A row is omitted if the condition evaluates to FALSE or NULL, effectively filtering the results based on specified criteria.