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SQL Problems and solutions S. I. Moiseenko

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SQL data manipulation language

SELECT statement

CASE statement page 4

Beginning from version 2012, IIF function is available in SQL(Structured Query Language) is a database computer language designed for the retrieval and management of data in relational database management systems (RDBMS), database schema creation and modification, and database object access control management.SQL Server. This function is well known to those who use Access Visual Basic for ApplicationsVBA and is an alternative to the CASE expression in standard SQL. The syntax of IIF function is

IIF(< condition>, < expression IF condition IS true>, < expression IF condition IS NOT true>)

The function returns the value of expression in the second parameter, if the condition is evaluated as true, or the value of expression in the third parameter otherwise. So, the function

IIF(condition, expression_1, expression_2)

is equivalent to the following CASE statement:

   CASE WHEN condition THEN expression_1 ELSE expression_2 END

Using IIF function, we can rewrite the solution of the first task as follows:

Console

Execute

SELECT DISTINCT product.model,
    IIF(price IS NULL,  'Not available', CAST(price AS CHAR(20))) price
    FROM Product LEFT JOIN
    PC ON Product.model = PC.model
    WHERE product.type = 'PC';

In the case where there are more than two variants of branching, you can use nested IIF functions. For example, solution for task 5.10.1 you can get with the following query:

Console

Execute

SELECT DISTINCT model, price,
    IIF(price=(SELECT MAX(price) FROM PC), 'Most expensive', 
        IIF(price=(SELECT MIN(price) FROM PC), 'Most cheap', 'Mean price')) comment
    FROM PC
    ORDER BY price;

If situation will go in the same manner, SWITCH statement could soon appear in T-SQL. :-)

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SQL Problems and solutions

S. I. Moiseenko

SQL data manipulation language

SELECT statement

CASE statement page 4