Order of the columns matter.

The index is useless if the first column doesn't appear in the WHERE clause.

Example 1:

An index on (t, x) will not be used in this query:

• SELECT * FROM table WHERE...

The German scientist was the first person to identify electromagnetic radiation in a wavelength that we today know as an x-ray.

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Smoking is the most common cause of heart disease. Smoking causes emphysema, cancer, gum disease, and harms almost every organ in your body. Tobacco smoke damages blood vessels, increases blood pressure, lowers HDL cholesterol, and causes peripheral artery disease and atherosclerosis.

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