GREATEST
eg：獲取所有記錄中，兩個(gè)字段的最大值:
SELECT
MAX(shang_times) AS shang,
MAX(xia_times) AS xia,
MAX(GREATEST(shang_times,xia_times)) AS max
FROM times_tb WHERE id = 2744;
LEAST
eg：獲取所有記錄中，兩個(gè)字段的最小值:
SELECT
MIN(shang_times) AS shang,
MIN(xia_times) AS xia,
MIN(LEAST(shang_times,xia_times)) AS min
FROM times_tb WHERE id = 2744;
