In this post I’m going to quickly explain how to use MySQL exit and quit and \q commands to return to the operating system’s command line shell.
When working with MySQL at the command line you’ll arrive at a point when you are finished working. Thus, you’ll want to exit mysql and return back to your operating system’s command shell. MySQL provides two keywords for doing this, namely, exit and quit as well as a shorthand version \q.
So for example, say you’re sitting at the mysql command line and it looks like this…
mysql>
And you wish to go back to your command shell…
mysql>exit
-OR-
mysql>quit
(Type either exit or quit and press enter)
You can also use some shorthand to exit or quit the command line. You can use the \q to quit as well.
It looks like this…
mysql>\q
(Type \q and press enter)
It’s as simple as that. Learning how to use the MySQL command line can be powerful and efficient. These three commands will help you on your way to using the command line more effectively.
What is a MySQL DECIMAL? Simply put, it is just a number that can have a decimal in it (2012.56 and -2013.0034 are examples). Let’s take a look at how to declare a MySQL DECIMAL.
DECIMAL(M, D)
M is the maximum number of digits (IE precision) and has a range from 1 to 65 (Take note that versions of MySQL prior to 5.0.3 allowed the range from 1 to 254). This is the total number of digits INCLUDING decimal digits.
D is the number of digits to the right of the decimal point (IE scale) and has a range from 0 to 30 AND cannot be larger than M.
Why use a MySQL DECIMAL?
You would generally use a decimal type when you need to store exact fractional values like money. It doesn’t suffer from the rounding errors of other number types in MySQL.
How do you use MySQL DECIMAL?
Here is some example mysql code…
CREATE DATABASE IF NOT EXISTS Testing;
USE Testing;
CREATE TABLE WeightCalculation (WeightCalculationID INT NOT NULL, Weight DECIMAL(10,5) NOT NULL);
INSERT INTO WeightCalculation (WeightCalculationID, Weight) VALUES (1,54.3445);
INSERT INTO WeightCalculation (WeightCalculationID, Weight) VALUES (2,928.23017);
SET @a = (SELECT SUM(WEIGHT) FROM WeightCalculation);
INSERT INTO WeightCalculation (WeightCalculationID, Weight) VALUES (3,@a);
SELECT * FROM WeightCalculation;
DROP DATABASE Testing;
So let walk through this code and see what is going on. To start, I create our Testing database if it doesn’t exist. Then I create a table called ‘WeightCalculation’ and give it two columns ‘WeightCalculationID’ and ‘Weight’ in order to store some simple data. Notice that column ‘Weight’ has been declare a DECIMAL of total length 10 digits and up to 5 decimal places. Next, I insert two rows of data into the table. Just for fun I calculate the sum of all the Weight column values and store them in a user-defined variable named @a then insert the sum into another row of the table. Lastly, I perform a SELECT operation on the table to get it’s contents. To clean up I drop the Testing database.
For further information check here. Check here for more examples of precision math.
