大约有 40,000 项符合查询结果（耗时：0.0340秒） [XML]
ORDER BY the IN value list
... (3,2),
(2,3),
(4,4)
) as x (id, ordering) on c.id = x.id
order by x.ordering
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What is the most efficient/elegant way to parse a flat table into a tree?
...d in the same table too. Read "Trees and Hierarchies in SQL for Smarties" by Joe Celko for a lot more information on these designs.
I usually prefer a design called Closure Table (aka "Adjacency Relation") for storing tree-structured data. It requires another table, but then querying trees is pre...
How to get ID of the last updated row in MySQL?
...= id)
WHERE some_other_column = 'blah' LIMIT 1;
SELECT @update_id;
EDIT by aefxx
This technique can be further expanded to retrieve the ID of every row affected by an update statement:
SET @uids := null;
UPDATE footable
SET foo = 'bar'
WHERE fooid > 5
AND ( SELECT @uids := CONCAT_WS('...
How to filter SQL results in a has-many-through relation
...NDEX sc_club_id_idx ON student_club (club_id);
club_pkey is not required by most queries here.
Primary keys implement unique indexes automatically In PostgreSQL.
The last index is to make up for this known shortcoming of multi-column indexes on PostgreSQL:
A multicolumn B-tree index can be us...
How to use GROUP_CONCAT in a CONCAT in MySQL
..., ':', group_concat(`Value` separator ',')) as `Name`
from mytbl
group by
id,
`Name`
) tbl
group by id;
You can see it implemented here : Sql Fiddle Demo. Exactly what you need.
Update
Splitting in two steps. First we get a table having all values(comma separated) against a unique[N...
MySQL INNER JOIN select only one row from second table
... SELECT user_ID, MAX(date) maxDate
FROM payments
GROUP BY user_ID
) b ON c.user_ID = b.user_ID AND
c.date = b.maxDate
WHERE a.package = 1
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Get specific object by id from array of objects in AngularJS
...ate over the array. Obviously if you are sure that the results are ordered by id you can do a binary search
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Get object by id()? [duplicate]
Let's say I have an id of a Python object, which I retrieved by doing id(thing) . How do I find thing again by the id number I was given?
...
How to find largest objects in a SQL Server database?
...d I go about finding the largest objects in a SQL Server database? First, by determining which tables (and related indices) are the largest and then determining which rows in a particular table are largest (we're storing binary data in BLOBs)?
...
How to select unique records by SQL
...
If you only need to remove duplicates then use DISTINCT. GROUP BY should be used to apply aggregate operators to each group
GROUP BY v DISTINCT
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