Using mysql as a Calculator
Problem
You need a quick way to evaluate an expression.
Solution
Use mysql as a calculator. MySQL
doesn’t require every SELECT
statement to refer to a table, so you can select the results of
arbitrary expressions.
Discussion
SELECT statements typically refer to some table or
tables from which you’re retrieving rows. However,
in MySQL, SELECT need not reference any table at all,
which means that you can use the mysql program as
a calculator for evaluating an expression:
mysql> SELECT (17 + 23) / SQRT(64);
+----------------------+
| (17 + 23) / SQRT(64) |
+----------------------+
| 5.00000000 |
+----------------------+This is also useful for checking how a comparison works. For example, to determine whether or not string comparisons are case sensitive, try the following query:
mysql> SELECT 'ABC' = 'abc';
+---------------+
| 'ABC' = 'abc' |
+---------------+
| 1 |
+---------------+The result of this comparison is 1 (meaning “true”; in general, nonzero values are true). This tells you that string comparisons are not case sensitive by default. Expressions that evaluate to false return zero:
mysql> SELECT 'ABC' = 'abcd';
+----------------+
| 'ABC' = 'abcd' |
+----------------+
| 0 |
+----------------+If the value of an expression cannot be determined, the result is
NULL:
mysql> SELECT 1/0;
+------+
| 1/0 |
+------+
| NULL |
+------+SQL variables may be used to store the results of intermediate calculations. The following statements use variables this way to compute ...