SELECT Expressions

The projection-list of a SELECT clause may contain column names, constants and/or expressions. It is sometimes advantageous to use an expression that incorporates data values from one or more columns. Any legal arithmetic expression involving column values, numeric or string constants, functions, and arithmetic operators is permitted in an expression. See Functions In SELECT Clauses. Parentheses may be used as necessary to define evaluation order.

Column names generally match those specified in the SELECT clause. In the case of expressions or column names made up of multiple words (column names over 30 characters long), the XDB Server substitutes the special name Columnn where the second n is the column number -- counting from the left side of the result display.

Numeric constants and string constants can be "selected" just like column names. String constants can be enclosed in single or double quotes. For instance, the query below uses a string constant in the SELECT statement:

SELECT "Supplier", sname, "is located in", city
FROM supplier

The previous query produces the following results display:

The query below uses an arithmetic expression in the SELECT clause to display shipping costs for each part received from London:

SELECT pno, weight * 1.15
FROM part
WHERE city = "LONDON"

The column rename feature can assign a name to a new column of output computed from an arithmetic expression. For example, the results of the following query would appear under two separate columns named PNO and shipcost:

SELECT pno, shipcost = weight * 1.15
FROM part
WHERE city = "LONDON"

SELECT SUM(qty)
FROM partsupp

More:

• CASE Expressions
• Concatenation
• Functions In SELECT Clauses
• Examples