mysql - 合并 MySQL 中的整个记录

Question

我目前正在 MySQL 查询中单独合并字段，但我想合并整个记录。

这可能吗？

SELECT la.id, 
COALESCE(( SELECT name FROM lookup_changed l0, 
           ( SELECT MAX(id) id 
             FROM lookup_changed     
             WHERE lookup_id = 26
           ) l1 
           WHERE l0.id = l1.id
         ), la.name) name,
COALESCE(( SELECT msisdn FROM lookup_changed l0, 
           ( SELECT MAX(id) id 
             FROM lookup_changed     
             WHERE lookup_id = 26
           ) l1 
           WHERE l0.id = l1.id
         ), la.msisdn) msisdn
FROM lookup_added la
WHERE la.id = 26

@Alma Do - 伪 SQL 是:

SELECT la.id, 
MULTICOALESCE(( SELECT <name, msisdn> FROM lookup_changed l0, 
                ( SELECT MAX(id) id 
                  FROM lookup_changed     
                  WHERE lookup_id = 26
                ) l1 
                WHERE l0.id = l1.id
              ), <la.name, la.msisdn>) <name, msisdn>
FROM lookup_added la
WHERE la.id = 26

Answer 1

由于 COALESCE()“返回第一个非 NULL 参数”，听起来您想检索“查询集中的第一个非 NULL 结果”:

-- syntax error
SELECT COALESCE(
    SELECT a FROM ta,
    SELECT b FROM tb
);

-- roughly equates to
( SELECT a AS val FROM ta WHERE a IS NOT NULL ORDER BY a LIMIT 1 )
UNION
( SELECT b AS val FROM tb WHERE b IS NOT NULL ORDER BY b LIMIT 1 )
ORDER BY val LIMIT 1 ;

评论:

• 我添加了 ORDER BY 子句，否则“第一行”没有任何意义
• 内部的 LIMIT 1 子句是可选的(但允许提前修剪子结果)
• 子查询周围的括号是强制性的