Question

查询3个表，最后一个表有一个额外的行要查找试过这个：

(SELECT 't1' AS tn, navid, clicks AS cc, tags 
FROM t1 
WHERE DATE_ADD(d, INTERVAL '0 8' DAY_HOUR) <= NOW() 
AND tags LIKE '%cars%' )

UNION DISTINCT

(SELECT 't2' AS tn, navid, clicks AS cc, tags 
FROM t2 
WHERE DATE_ADD(d, INTERVAL '0 8' DAY_HOUR) <= NOW() 
AND tags LIKE '%cars%' )

UNION DISTINCT

(SELECT 't3' AS tn, navid, title, clicks AS cc, tags 
FROM t3 
WHERE DATE_ADD(d, INTERVAL '0 8' DAY_HOUR) <= NOW() 
AND tags LIKE '%cars%' )

我想在t3中获得title字段任何帮助，谢谢

Answer 1

只需将它添加到前两个子查询中，其值为NULL：

(SELECT 't1' AS tn, navid, NULL as title, clicks AS cc, tags 
 FROM t1 
 WHERE DATE_ADD(d, INTERVAL '0 8' DAY_HOUR) <= NOW() 
       AND tags LIKE '%cars%' )
UNION DISTINCT
(SELECT 't2' AS tn, navid, NULL as title, clicks AS cc, tags 
 FROM t2 
 WHERE DATE_ADD(d, INTERVAL '0 8' DAY_HOUR) <= NOW() 
       AND tags LIKE '%cars%' )
UNION DISTINCT
(SELECT 't3' AS tn, navid, title, clicks AS cc, tags 
 FROM t3 
 WHERE DATE_ADD(d, INTERVAL '0 8' DAY_HOUR) <= NOW() 
       AND tags LIKE '%cars%' )

Answer 2

由UNION组合的SQL应具有相同的列数和类型。

这是因为您只有一个查询结果，即使它看起来像多个小查询。

因此，您必须为title列添加一些值。您在t1和t2中没有它。所以只需选择null：

SELECT 't1' AS tn, navid, null as title, clicks AS cc, tags ...

(SELECT 't1' AS tn, navid, null as title, clicks AS cc, tags 
FROM t1 
WHERE DATE_ADD(d, INTERVAL '0 8' DAY_HOUR) <= NOW() 
AND tags LIKE '%cars%' )

UNION DISTINCT

(SELECT 't2' AS tn, navid, null as title, clicks AS cc, tags 
FROM t2 
WHERE DATE_ADD(d, INTERVAL '0 8' DAY_HOUR) <= NOW() 
AND tags LIKE '%cars%' )

UNION DISTINCT

(SELECT 't3' AS tn, navid, title, clicks AS cc, tags 
FROM t3 
WHERE DATE_ADD(d, INTERVAL '0 8' DAY_HOUR) <= NOW() 
AND tags LIKE '%cars%' )

Answer 3

您必须为UNION提供相同数量的列，并且列名称基于第一个查询，因此您无需为UNION中的每个查询命名列

(SELECT 't1' AS tn, navid, '' As title, clicks AS cc, tags 
FROM t1 
WHERE DATE_ADD(d, INTERVAL '0 8' DAY_HOUR) <= NOW() 
AND tags LIKE '%cars%' )

UNION DISTINCT

(SELECT 't2', navid, '', clicks, tags 
FROM t2 
WHERE DATE_ADD(d, INTERVAL '0 8' DAY_HOUR) <= NOW() 
AND tags LIKE '%cars%' )

UNION DISTINCT

(SELECT 't3', navid, title, clicks, tags 
FROM t3 
WHERE DATE_ADD(d, INTERVAL '0 8' DAY_HOUR) <= NOW() 
AND tags LIKE '%cars%' )

sql union不规则组合

3 个答案: