![]() The SQL standard does not specify how to process case expressions-it just defines the result. 1 If else is omitted, else null is implicit. īefore closing the case expression with end, the optional else clause can be used. 0 Put simply: case expressions evaluate to the of the first true. To close that gap, SQL uses the order in which the conditions appear in the case expression to define their precedence. A flat case expression does not have such an inherent precedence. On the other hand, nesting provides an inherent precedence among the conditions. This allows for multiple conditions even without nesting-unlike the ?: operator in other programming languages. is an arbitrary SQL expression: it can be a simple expression like a constant or column name, or also a complex SQL expression containing subqueries and, of course, nested case expressions.Ī case expression can contain several when- then pairs. Note that is a condition like those in where clauses-for example: column_name IS NULL. ![]() From that point of view, one could say that searched case is the only case syntax you absolutely need to remember. Furthermore searched case works in virtually all SQL databases. ![]() The other variants are abbreviations that could also be written as searched case. The following example shows the syntax in the most generic form-the so-called searched case. The syntax of the case expression is very flexible and allows for some abbreviations. Its use is similar to the ternary operator ?: in other programming languages. Being an expression-rather than a control structure-means that case varies the result of formulas (expressions) based on conditions. Nevertheless, SQL has something similar: the case expression. SQL is a declarative language: it does not provide control over program flow like if does for imperative programs.
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