U0400037: GaussDB does not support non-aggregation columns that are not in the GROUP BY clause in SELECT by default

The GROUP BY clause groups query results based on the values of one or more columns. The query results with the same value are in the same group. If the SELECT list expression references fields that are not grouped, this error is reported unless aggregate functions are used, because multiple values may be returned from ungrouped fields. The query result is uncertain. For example:

SELECT id, code FROM test_code group by code;

When the GROUP BY clause is omitted and the aggregate function is used, the entire query result set is considered as a large group. In this case, if both the aggregate function and common columns exist in the SELECT list, this error is reported. For example:

SELECT max(id), code FROM test_code;

If the value of sql_mode in MySQL does not contain ONLY_FULL_GROUP_BY, the preceding two queries are supported. The query results of non-aggregation columns that are not in the GROUP BY clause are uncertain. In MySQL 5.7 and later versions, ONLY_FULL_GROUP_BY is added for sql_mode by default.