Comparison operators

At the heart of every condition is a comparison of two values. The scribe asks: "Is the price greater than 30? Does the year of publication equal 1990?". In MySQL we answer such questions with comparison operators.

The six operators

| Operator | Meaning | Example | |----------|---------|---------| |

=

| equal |

cena = 30

| |

<>

| not equal |

kraj <> 'Polska'

| |

<

| less than |

rok_wydania < 1900

| |

>

| greater than |

cena > 50

| |

<=

| less than or equal |

cena <= 20

| |

>=

| greater than or equal |

rok_wydania >= 2000

|

Note, @name: in MySQL we check equality with a single

=

sign (not

==

as in JavaScript). Inequality is written as

<>

.

Example: expensive books

1SELECT * FROM ksiazki
2WHERE cena > 50;

This means: "Show all books whose price exceeds 50 coins".

Less, greater and their "or equal" variants

The operators

<=

and

>=

also include the boundary value. The condition

cena <= 20

returns both books cheaper than 20 coins and those costing exactly 20:

1SELECT * FROM ksiazki
2WHERE cena <= 20;

And the condition

rok_wydania >= 2000

also includes the year 2000 itself:

1SELECT * FROM ksiazki
2WHERE rok_wydania >= 2000;

Remember a simple rule: a

<

or

>

sign without a line does not include the boundary, but with a line

<=

/

>=

it does include it. A small difference, but it can change the whole result!