子查询还是连接？
我想知道是否有人可以向我解释何时使用子查询以及何时使用联接。
例如。
我有以下查询：
SELECT * from contacts where id in (select contactId from contactgrouplink where groupId = 1);
对此子查询进行联接有什么好处？
I am wondering if anyone can explain to me when you would use a sub query and when you would use a join.
for example.
I have this query:
SELECT * from contacts where id in (select contactId from contactgrouplink where groupId = 1);
What would the benefit be of a join over this sub query?
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子查询与连接
Look at here well discussed
Subqueries vs joins
在每个查询之前使用 EXPLAIN 来查看查询的作用！
Use EXPLAIN just before each of those query's... to see what query does!
做一个解释，我的经验法则是尝试摆脱 DEPENDENT SUBQUERY，因为这意味着对于外部 SQL 语句中的每一行，都会执行一个查询。此外，您可以尝试将其实现为联接，并查看每个版本将检查多少行并从那里进行调用。
Do an EXPLAIN, my rule of thumb is to try to get rid of DEPENDENT SUBQUERY since that means for each row in the outer SQL statement, a query is executed. Also, you can try to implement it as a join and see how many rows each version would examine and make the call from there.
据我所知，子查询比 join 更好。
我还使用子查询，因为“加入”会影响性能。 （根据My-Sql偏好）
In my knowledge, Sub-query is batter than join .
I'm also use Sub-query Becoz "Join" is Effecting performance. (According My-Sql Preference)