table1 UNION ALL table2是否保证输出顺序table1，table2？ [英] Does table1 UNION ALL table2 guarantee output order table1, table2?

问题描述

SELECT a FROM b
UNION ALL 
SELECT a FROM c
UNION ALL 
SELECT a FROM d

UNION ALL是否保证按顺序打印表b，c，d中的记录？也就是说，c之前没有记录，b之前没有记录。这个问题不是针对特定的DBMS的。

Does UNION ALL guarantee to print out records from tables b, c, d in that order? I.e., no records from c before any from b. This question is not for a specific DBMS.

推荐答案

无序，无序保证-适用于每个数据库。

No order by, no order guarantee whatsoever - that's for every database.

对于标准SQL，将ORDER BY应用于所有联合查询的结果。

And for standard SQL, an ORDER BY is applied to the results from all the unioned queries.

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