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Is it possible to GROUP BY multiple columns using MySQL?
Is it possible to GROUP BY more than one column in a MySQL SELECT query? For example:
7 Answers
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What's the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN and FULL JOIN? [duplicate]
...These pictures don't do it for me. Why is the top right picture not simply SELECT * FROM TableA;? Why is the top left picture not simply SELECT * FROM TableB;? Why is the top middle picture not SELECT * FROM A INTERSECT SELECT * FROM B ? etc
– onedaywhen
Sep 9 ...
PreparedStatement IN clause alternatives?
... and cons of each is available here.
The suggested options are:
Prepare SELECT my_column FROM my_table WHERE search_column = ?, execute it for each value and UNION the results client-side. Requires only one prepared statement. Slow and painful.
Prepare SELECT my_column FROM my_table WHERE search_...
SQL JOIN and different types of JOINs
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There are relatively new LATERAL JOIN .. SELECT * FROM r1, LATERAL fx(r1)
– Pavel Stehule
Jul 30 '13 at 11:52
13
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Multiple select statements in Single query
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SELECT (
SELECT COUNT(*)
FROM user_table
) AS tot_user,
(
SELECT COUNT(*)
FROM cat_table
) AS tot_cat,
(
SELECT COUNT(*)
FROM course_table
) AS tot_course
...
What is the difference between “INNER JOIN” and “OUTER JOIN”?
...he intersection of the two tables, i.e. the two rows they have in common.
select * from a INNER JOIN b on a.a = b.b;
select a.*, b.* from a,b where a.a = b.b;
a | b
--+--
3 | 3
4 | 4
Left outer join
A left outer join will give all rows in A, plus any common rows in B.
select * from a LEFT OUT...
MySQL - SELECT WHERE field IN (subquery) - Extremely slow why?
...
Rewrite the query into this
SELECT st1.*, st2.relevant_field FROM sometable st1
INNER JOIN sometable st2 ON (st1.relevant_field = st2.relevant_field)
GROUP BY st1.id /* list a unique sometable field here*/
HAVING COUNT(*) > 1
I think st2.relevant_...
LR性能测试结果样例分析 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...是否达到了预期的性能指标，其中又有哪些性能隐患，该如何解决。
图1- 1性能测试结果分析流程图
结果摘要
LoadRunner进行场景测试结果收集后，首先显示的该结果的一个摘要信息，如图1- 2所示。概要中列出了场景执行...
企业级负载平衡简介 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...务器。该设备会根据其内部所包含的请求分发逻辑来决定如何对这些请求进行分发，以避免出现单个服务器过载的情况。这些用来对请求进行分发的设备实际上就是负载平衡服务器。
当然，我们不会等到服务器真正过载了才去...
Rename MySQL database [duplicate]
...be found using a
query on information_schema.TABLES table.
mysql> select TABLE_NAME from information_schema.tables where
table_schema='<old_schema_name>' and TABLE_TYPE='BASE TABLE';
3) Dump the views in an out file. Views can be found using a query on
the same information_...