如何在SQL中加入相同的表？

Question

我想在表B中加入表A的类别列。如何在同一表中编写该联接？

这是表A的sql脚本

select code_id, code_desc category
FROM t_setup_code 
WHERE code_id IN (select code_1 from t_setup_code WHERE code_desc LIKE 'Ag%');

这是表B的sql脚本

SELECT a.plot_sub_usage, b.code_id, b.code_1, b.code_desc, COUNT(*)
FROM dc_plot a, t_setup_code b
WHERE a.plot_sub_usage = b.code_id
AND b.code_id LIKE 'LUC-AG%'
GROUP BY a.plot_sub_usage, b.code_desc, b.code_id, b.code_1
ORDER BY a.plot_sub_usage;

这是两个sql脚本的结果

结果应如下所示：

Answer 1

尝试一下

SELECT a.plot_sub_usage, b.code_desc, c.code_desc, COUNT(*)
FROM dc_plot a 
        inner join t_setup_code b on a.plot_sub_usage = b.code_id
        inner join t_setup_code c on c.code_id = b.code_1
WHERE b.code_id LIKE 'LUC-AG%'
AND c.code_desc like 'Ag%'
GROUP BY a.plot_sub_usage, b.code_desc, c.code_desc
ORDER BY a.plot_sub_usage;