Mysql case when is null then

We can execute a query like. Skip to content. Report a Bug. Previous Prev. Next Continue. Home Testing Expand child menu Expand. SAP Expand child menu Expand. Web Expand child menu Expand. Furthermore searched case works in virtually all SQL databases.

From that point of view, one could say that searched case is the only case syntax you absolutely need to remember. Thus the name searched case. A case expression can contain several when - then pairs. This allows for multiple conditions even without nesting—unlike the?

On the other hand, nesting provides an inherent precedence among the conditions. A flat case expression does not have such an inherent precedence. To close that gap, SQL uses the order in which the conditions appear in the case expression to define their precedence.

Before closing the case expression with end , the optional else clause can be used. The SQL standard does not specify how to process case expressions—it just defines the result. Of course, these products eventually deliver the right result—they just discard the unnecessarily evaluated ones.

Ultimately, this is a result of the declarative nature of SQL: the database—not the programmer—decides how to get the correct result. Do not use non-deterministic functions or data-changing functions in case expressions.

The undefined evaluation process can have unpredictable side effects. To avoid repeating an operand that is used in all when clauses over and over again, the SQL standard offers the so-called simple case :.

The other side of the comparison remains in the when clause. The standard defines the simple case as a transformation to a searched case —the rules described above remain valid.

SQL offers two case abbreviations to cope with null : coalesce and nullif. Both are used like functions and do not use the keywords case , when , then , else and end. Coalesce returns the first not- null parameter or null , if all parameters are null.

The number of parameters is not limited. The standard defines coalesce as a transformation into a case expression. The following expressions are therefore equivalent:.

Nullif requires two parameters and generally returns the value of the first one. Nullif is also defined as a transformation to case and is typically used to prevent division by zero errors:. I make my living from training , other SQL related services and selling my book. SQL has introduced two more abbreviations that extend the simple case. Add a comment. Active Oldest Votes. Improve this answer. John Woo John Woo k 63 63 gold badges silver badges bronze badges. Thanks for your help — user This adds an implicit assumption to your code, namely that some column will never take the value 0 or 3.

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