Expressions are a common element of SQL statements, and they occur in many contexts. For example, expressions often occur in the WHERE clause of SELECT, DELETE, or UPDATE statements to identify which records to retrieve, delete, or update. But expressions may be used in many other places; for example, in the output column list of a SELECT statement, or in ORDER BY or GROUP BY clauses. Terms of expressions consist of constants (literal numbers, strings, dates, and times), NULL values, references to table columns, and function calls. Terms may be combined using operators into more complex expressions. Many types of operators are available, such as those for arithmetic, comparison, logical, and pattern-matching operations. Here are some examples of expressions:
All these types of values can be combined into more complex expressions to produce other values of interest. The following statement demonstrates this: mysql> SELECT Name, -> TRUNCATE(Population/SurfaceArea,2) AS 'people/sq. km', -> IF(GNP > GNPOld,'Increasing','Not increasing') AS 'GNP Trend' -> FROM Country ORDER BY Name LIMIT 10; +---------------------+---------------+----------------+ | Name | people/sq. km | GNP Trend | +---------------------+---------------+----------------+ | Afghanistan | 34.84 | Not increasing | | Albania | 118.31 | Increasing | | Algeria | 13.21 | Increasing | | American Samoa | 341.70 | Not increasing | | Andorra | 166.66 | Not increasing | | Angola | 10.32 | Not increasing | | Anguilla | 83.33 | Not increasing | | Antarctica | 0.00 | Not increasing | | Antigua and Barbuda | 153.84 | Increasing | | Argentina | 13.31 | Increasing | +---------------------+---------------+----------------+ The expressions in the preceding statement use these types of values:
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