Expressions are the elementar building-blocks of SQL-Queries; most SQL-Clauses (e.g., SELECT, WHERE) use them as arguments. An expression is either a value (e.g., 3, 2.3, 'hello world' or column_name), an operator (e.g., +, -, /), or a function (e.g., my_function()
).
Some operations, and most functions, work only on specific data types. For example, there are a number of operators and functions specifically for dates and strings.