Retrieving Computed Values

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You can retrieve computed values by using arithmetic, string and boolean operators in the SELECT clause of the statement.

When retrieving computed values, parentheses can be used to force the operation priority.

Without parentheses, the normal precedence rules apply, i.e. first multiplication and division are performed, then addition and subtraction, then comparisons and finally AND and OR. Operators with the same precedence are evaluated from left to right.

The following computational operators may be used:

Operator	Explanation
+	addition
-	subtraction
*	multiplication
/	division
||	string concatenation

See the Mimer SQL Reference Manual, SQL Syntax Elements, for information regarding the type and precision of the result of an arithmetic expression.

Show the exchange rate for the US Dollar if there was a -10% change:

 SELECT exchange_rate, exchange_rate * 0.90
    FROM  currencies
    WHERE code = 'USD';

Returns:

EXCHANGE_RATE
0.8711	0.783990

Evaluating Boolean Expressions

Boolean expressions return a truth value (TRUE or FALSE), depending on the result of one or more boolean expressions.

Specify when the exchange rate is less than 1 or the currency code is "ALL":

 SELECT currency,
        exchange_rate < 1.0 or code = 'ALL'
    FROM currencies;

Returns:

currency
UAE Dirhams	FALSE
Afghanis	FALSE
Leke	TRUE
Armenian Drams	-
Netherlands Antillian Guilders	FALSE
Kwanza	-
Argentine Pesos	TRUE
Australian Dollars	FALSE
...	...

Labels and Computed Values

The computed column is unnamed by default in the result table. A label may be used to provide a name.

For example:

 SELECT exchange_rate, exchange_rate * 0.90 AS new_exchange_rate
    FROM currencies
    WHERE code = 'USD';

Returns:

EXCHANGE_RATE	NEW_EXCHANGE_RATE
0.8711	0.783990

Constant Values

A column may also be computed as a constant value, which adds an extra column to the result table.

For example:

 SELECT exchange_rate, '10% reduction:',
        exchange_rate * 0.90 AS new_exchange_rate
    FROM currencies
    WHERE code = 'USD';

Returns:

EXCHANGE_RATE		NEW_EXCHANGE_RATE
0.8711	10% reduction:	0.783990

You may also retrieve a value computed using the values in two or more columns, providing that the data types are compatible.

Retrieve the currencies prefixed with the word "Currency:":

 SELECT 'Currency: ' || currency
    FROM currencies
    WHERE code LIKE 'A%';

Returns:

Currency: UAE Dirhams
Currency: Afghanis
Currency: Leke
Currency: Armenian Drams
Currency: Netherlands Antillian Guilders
Currency: Kwanza
...

Padding Concatenated Strings

For string concatenation, column values are padded with trailing blanks to the length of the column definition, if the column data type is fixed-length (CHARACTER or NATIONAL CHARACTER).

For example:

 SELECT currency || 'Currency'
    FROM currencies
    WHERE code LIKE 'A%';

Returns:

UAE Dirhams Currency
Afghanis Currency
Leke Currency
Armenian Drams Currency
Netherlands Antillian Guilders Currency
Kwanza Currency
...

(If the column data type is variable length, i.e. VARCHAR or NCHAR VARYING, no blank padding is performed.)

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