How to use WHERE statements in MySQL

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Empower your queries to refine database searches with MySQL WHERE statements.

Inside the realm of MySQL database admin, you’ll sooner or later end up sifting via the large assortment of knowledge present in your information heart databases. That is all effective and good when you’ve gotten a GUI instrument for the duty.

However what if you might want to drop to the command line? What do you do? You make use of WHERE statements. What’s a A WHERE assertion? Easy. This instrument is utilized in MySQL queries to filter data in order that they meet a particular situation. Any rows that don’t meet the desired situation are eradicated from the outcomes of the question. WHERE statements are very helpful to make use of, and I will present you ways.

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What you want

To make this work, you want an set up of MySQL server up and working. I will assume you’ve gotten that obtainable. I may even assume you’ve gotten information in your MySQL server. If not, observe the steps in The best way to add information into MySQL tables from the command line (I will truly observe the instance proven in that article).

With that stated, let’s get to work.

Utilizing the database

Within the above talked about piece, we created a database known as TECHREPUBLIC and added information to it. With a purpose to make use of the WHERE assertion, we should first change to the TECHREPUBLIC database. So log into your MySQL immediate with the command:

mysql -u root -p

Should you get an error, when making an attempt to log in to the MySQL immediate, you may need to as an alternative concern the command:

sudo mysql -u root -p

Change to the TECHREPUBLIC database with the command:

USE TECHREPUBLIC;

You must now see that you’re utilizing the right database (Determine A).

Determine A: We have modified to the TECHREPUBLIC database.

SELECT and WHERE

With a purpose to use the WHERE assertion, you should first know the best way to use the SELECT assertion. What this assertion does is specify, which columns to learn information from. So, in our TECHREPUBLIC database we now have a desk known as MEMBERS2. In that desk we now have columns:

Say we wish to view an entry within the lastname column that incorporates ‘wallen.’ To try this, we use each the SELECT and WHERE statements, such that SELECT instructs the question to pick out from the lastname column and WHERE says to filter out each occasion however these that don’t equal a specified string. With WHERE statements you’ll be able to take a look at for the next:

  • Equality, utilizing =.
  • Inequality, utilizing !=.
  • Much less-than, utilizing <.
  • Much less-than or equal-to, utilizing <=.
  • Better than, utilizing >.
  • Better than or equal to, utilizing >=.
  • BETWEEN
  • IN
  • EXISTS
  • LIKE
  • IS NULL
  • IS NOT NULL

For our instance, we’ll use the equality take a look at.

So, bear in mind, we’re testing the lastname column, within the MEMBERS2 desk, for entries which can be equal to ‘wallen’. Here is how to do this (from the MySQL immediate):

SELECT * FROM MEMBERS2 WHERE lastname = 'wallen';

The outcomes will present solely these entries whose lastname column is the same as ‘wallen’ (Determine B).

Figure BFigure B

Determine B: Our first WHERE assertion.

If you wish to filter out all entries with the final title ‘wallen’, you possibly can use the inequality filter like so:

SELECT * FROM MEMBERS2 WHERE lastname != 'wallen';

The outcomes from that question (Determine C) will record all entries however these whose lastname column embody ‘wallen’.

Figure CFigure C

Determine C: Our inequality take a look at utilizing the WHERE assertion.

Utilizing Wildcards

As an instance, for instance, which you could’t bear in mind the total final title, however you already know it begins with a ‘w’. How do you employ a WHERE assertion to provide such an entry? With a wildcard. For MySQL, the wildcard is the % character. With a purpose to make use of the wildcard, you can’t use the equality take a look at. As a substitute you should use the LIKE take a look at, as such:

SELECT * FROM MEMBERS2 WHERE lastname LIKE 'w%';

The outcomes will show any lastname column entry that begins with a w (Determine D).

Figure DFigure D

Determine D: Utilizing a wildcard with a WHERE assertion.

And that is the gist of utilizing the WHERE assertion with MySQL. When you do not have the facility of a user-friendly GUI, and you might want to seek for information, this assertion will turn into extremely helpful.

Additionally see

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Picture: Jack Wallen

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