加油，新时代打工人！

思路：
先查出有数据的县区，用县区编码判断，不存在县区里的数据。然后，用union all进行两个SQL拼接起来。

SELECT
	t.regionCode,
	t.regionName,
	t.testNum,
	t.sampleNum,
	t.squareNum,
	t.cropsCatgoryNum
FROM
	(
		(
		SELECT
			ar.`code` AS regionCode,
			ar.full_name AS regionName,
			count( tm.id ) AS testNum,
			IFNULL( sum( tm.sample_num ), 0 ) AS sampleNum,
			FORMAT( IFNULL( sum( tm.fields_square )/ 1000, 0 ), 3 ) AS squareNum,
			tc.crops_id AS cropsCatgoryNum 
		FROM
			t_adminregion ar
			LEFT JOIN t_test_main tm ON SUBSTRING( tm.village, 1, 6 ) = SUBSTRING( ar.`code`, 1, 6 )
			LEFT JOIN t_test_crops tc ON tc.test_id = tm.id 
		WHERE
			ar.`level` = 22 
			AND MONTH ( tm.create_time ) = 1 
		GROUP BY
			ar.`code` 
		ORDER BY
			ar.`code` 
		) UNION ALL
	SELECT
		t1.CODE,
		t1.full_name,
		0 AS TestNum,
		0 AS SampleNum,
		0 AS SquareNum,
		0 AS CropsCatgoryNum 
	FROM
		t_adminregion t1
		LEFT JOIN (
		SELECT
			ar.`code` AS regionCode,
			ar.full_name AS regionName,
			count( tm.id ) AS testNum,
			IFNULL( sum( tm.sample_num ), 0 ) AS sampleNum,
			FORMAT( IFNULL( sum( tm.fields_square )/ 1000, 0 ), 3 ) AS squareNum,
			tc.crops_id AS cropsCatgoryNum,
			tm.create_time AS createTime 
		FROM
			t_adminregion ar
			LEFT JOIN t_test_main tm ON SUBSTRING( tm.village, 1, 6 ) = SUBSTRING( ar.`code`, 1, 6 )
			LEFT JOIN t_test_crops tc ON tc.test_id = tm.id 
		WHERE
			ar.`level` = 22 
			AND MONTH ( tm.create_time ) = 1 
		GROUP BY
			ar.`code` 
		ORDER BY
			ar.`code` 
		) a ON t1.CODE = a.regionCode 
	WHERE
		a.regionCode IS NULL 
		AND t1.`level` = 22 
	) t 
GROUP BY
	t.`regionCode` 
ORDER BY
	t.`regionCode`