Why does DISTINCT has to go first in MySQL?

问题

I have a query that works when I do

SELECT DISTINCT(table.field.id), 1 FROM ... 

but fails when I do

SELECT 1, DISTINCT(table.field.id) FROM ... 

Is this a known behavior?

Why does the first one work while the second doesn't?

回答1:

Unfortunately I'm not able to add a comment yet.

What @Gordon Linoff has written is exactly right. You are getting error as DISTINCT in general works as part of SELECT clause or AGGREGATE function. It is used to return unique rows from a result set and it can be used to force unique column values within an aggregate function.

Examples: SELECT DISTINCT * ... COUNT(DISTINCT COLUMN) or SUM(DISTINCT COLUMN).

More information's about DISTINCT in popular DB engines:

• PostgreSQL:https://www.postgresql.org/docs/9.0/static/sql-select.html#SQL-DISTINCT
• SQL Server: https://www.techonthenet.com/sql_server/distinct.php
• Oracle: https://www.techonthenet.com/oracle/distinct.php
• MySQL: https://dev.mysql.com/doc/refman/5.7/en/distinct-optimization.html https://dev.mysql.com/doc/refman/5.7/en/select.html

来源：https://stackoverflow.com/questions/43193406/why-does-distinct-has-to-go-first-in-mysql