SQL Expressions
SQL expressions specify a value, allowing you to perform arithmetic and logical operations and to generate new values or Boolean results from literals and stored values. An expression can consist of any of the following things:
Types of Expressions
SQL expressions generally fall into the following categories.
|
Type |
Description |
|
Numeric expression |
Expressions are generally classified by the type of result they produce. For example, a numeric expression consists of a column name, literal, function, or combination of column names, literals, and functions connected by arithmetic operators where the result is a numeric type. |
|
String expression |
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DateTime expression |
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Interval expression |
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Period expression, including a derived period |
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CASE expression |
A CASE expression consists of a set of WHEN/THEN clauses and an optional ELSE clause. A valued CASE expression tests for the first WHEN expression that is equal to a test expression and returns the value of the matching THEN expression. If no WHEN expression is equal to the test expression, CASE returns the ELSE expression, or, if omitted, NULL. A searched CASE expression tests for the first WHEN expression that evaluates to TRUE and returns the value of the matching THEN expression. If no WHEN expression evaluates to TRUE, CASE returns the ELSE expression, or, if omitted, NULL. |
Examples of Expressions
|
Expression |
Description |
'Test Tech'
|
Character string literal |
1024
|
Numeric literal |
Employee.FirstName
|
Column name |
Salary * 12 + 100
|
Arithmetic expression producing a numeric value |
INTERVAL '10' MONTH * 4
|
Interval expression producing an interval value |
CURRENT_DATE + INTERVAL '2' DAY
|
DateTime expression producing a DATE value |
CURRENT_TIME - INTERVAL '1' HOUR
|
DateTime expression producing a TIME value |
'Last' || ' Order'
|
String expression producing a character string value |
CASE x
WHEN 1
THEN 1001
ELSE 1002
END
|
Valued CASE conditional expression producing a numeric value |