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2.2 Value Expressions

Value expressions are used in a variety of contexts, such as in the target list of the SELECT command, as new column values in INSERT or UPDATE, or in search conditions in a number of commands. The result of a value expression is sometimes called a scalar, to distinguish it from the result of a table expression (which is a table). Value expressions are therefore also called scalar expressions (or even simply expressions). The expression syntax allows the calculation of values from primitive parts using arithmetic, logical, set, and other operations.

A value expression is one of the following:

• A constant or literal value.
• A column reference.
• A positional parameter reference, in the body of a function definition or prepared statement.
• A subscripted expression.
• A field selection expression.
• An operator invocation.
• A function call.
• An aggregate expression.
• A type cast.
• A scalar subquery.
• An array constructor.
• A row constructor.
• Another value expression in parentheses, useful to group subexpressions and override precedence.

In addition to this list, there are a number of constructs that can be classified as an expression but do not follow any general syntax rules. These generally have the semantics of a function or operator and are explained in the appropriate location in section 7 Functions and Operators. An example is the IS NULL clause.

We have already discussed constants in section 2.1.2 Constants. The following sections discuss the remaining options.