How to round down to nearest integer in MySQL?

Use FLOOR().

It will to round your decimal to the lower integer. Examples:

SELECT FLOOR(1.9) /* return 1 */
SELECT FLOOR(1.1) /* return 1 */

Other useful rounding

If you want to round your decimal to the nearest integer, use ROUND(). Examples:

SELECT ROUND(1.9) /* return 2 */
SELECT ROUND(1.1) /* return 1 */

If you want to round your decimal to the upper integer, use CEILING(). Examples:

SELECT CEILING(1.9) /* return 2 */
SELECT CEILING(1.1) /* return 2 */

Use FLOOR:

SELECT FLOOR(your_field) FROM your_table