SQL Expressions is a clause that can be used for return values. There are 4 types of SQL Expressions-
- Case Expressions – In this expression the user can use IF – THEN – ELSE logic without write procedure.
- Function Expressions – SQL built-in-functions can be used as Expressions.
- Aggregate Expressions – In This Expression aggregate functions is used to calculate a single value from the values of multiple rows for a column.
| Aggregate Name | Description |
| COUNT | Count the Number of rows returned by the query. |
| MIN | Return the minimum value of the expression. |
| MAX | Return the maximum value of the expression. |
| SUM | Return the sum of expressions. |
| AVG | Return the arithmetical mean of expressions. |
| STDDEV | Return the Standard Deviation of given expressions as the square root of VARIANCE function. |
| VAR | Return the variance of expressions as the square of standard deviation |
- Subqueries in Expression – A subquery is a select statement enclosed in parentheses and used in a main select statement as input.