Today I wrote such a SQL statement in Mysql on my personal server:

select id,name,link,passwd,original,type from movie GROUP BY link;

The execution even reported an error, the error information is as follows:

[2018-07-06 14: 53: 27.339] [000172] [Personal Online Database] [MYSQL]
1055 - Expression #1 of ORDER BY clause is not in GROUP BY clause and contains nonaggregated column 'information_schema.PROFILING.SEQ' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

My Mysql version is 5.7.22, which was newly installed when I was doing my personal project recently. This SQL is implemented in my company's server mysql (version 5.6). There is nothing wrong with it, because the usage of the group by statement is: group by The following fields need to appear after the select or use aggregate functions. The official website checks the explanation of sql_mode = only_full_group_by as follows:

ONLY_FULL_GROUP_BY

Reject queries for which the select list, HAVING condition, or ORDER BY list refer to nonaggregated columns that are neither named in the GROUP BY clause nor are functionally dependent on (uniquely determined by) GROUP BY columns.

As of MySQL 5.7.5, the default SQL mode includes ONLY_FULL_GROUP_BY. (Before 5.7.5, MySQL does not detect functional dependency and ONLY_FULL_GROUP_BY is not enabled by default. For a description of pre-5.7.5 behavior, see the MySQL 5.6 Reference Manual.)

A MySQL extension to standard SQL permits references in the HAVING clause to aliased expressions in the select list. Before MySQL 5.7.5, enabling ONLY_FULL_GROUP_BY disables this extension, thus requiring the HAVING clause to be written using unaliased expressions. As of MySQL 5.7.5, this restriction is lifted so that the HAVING clause can refer to aliases regardless of whether ONLY_FULL_GROUP_BY is enabled.

In other words, before 5.7.5, MySQL did not detect functional dependencies, only_full_group_by is not enabled by default, only_full_group_by means that the field of your group by must exactly match the field after the selection (except for aggregation functions) ).

Check the value of the sql_mode attribute in my mysql:

show variables like '%sql_mode%'

The following command resets the value of the sql_mode attribute:

 set session sql_mode='';

I set it to empty directly here. For the specific value of sql_mode, please refer to the official website:sql_mode attribute and value of mysql

Re-execute SQL, OK!

References for this article:mysql official website