大约有 6,000 项符合查询结果（耗时：0.0355秒） [XML]
MySQL order by before group by
... table, on both values you will return the full details of that post.
See SQL Fiddle with Demo.
To expand on my comments about using a subquery to accurate return this data.
MySQL does not force you to GROUP BY every column that you include in the SELECT list. As a result, if you only GROUP BY ...
Subqueries vs joins
...dependent of the containing query) will execute once at the beginning. The SQL engine makes this distinction automatically.
But, yeah, explain-plan will give you the dirty details.
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Declaring a default constraint when creating a table
I am creating a new table in Microsoft SQL server 2000 by writing the code instead of using the GUI, I am trying to learn how to do it "the manual way".
...
Why is iterating through a large Django QuerySet consuming massive amounts of memory?
...hanks for the great answer, @eternicode. In the end we dropped down to raw SQL for the desired database-level iteration.
– davidchambers
Aug 13 '11 at 21:15
2
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【内核源码】linux UDP实现 - 操作系统(内核) - 清泛网 - 专注C/C++及内核技术
...址的情况下，有可能导致单个链表的上有很多socket，导致查询慢
添加第二个hash表，使用地址和端口作为key， 来应对上述情况。 查询的时候只用查两个hash链表中较短的那个。
udp sencondary hash
connect()
sys_connect()->inet_dgram_connect...
Condition within JOIN or WHERE
...eports joining 5-6 tables on few millions records. Perf improves by 30% - sql server 2012
– Shahdat
Oct 6 '16 at 16:33
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LINQPad [extension] methods [closed]
...teXhtmlWriter - creates a text writer that uses LINQPad's Dump() formatter
SqlOutputWriter - returns the text writer that writes to the SQL output window
GetMyQueries, GetSamples - returns a collection of objects representing your saved queries / samples (for an example, execute a search using Edit ...
how perform grep operation on all files in a directory
...use then you can really see what files it's operating on:
find . -name "*.sql" -exec grep -H "slow" {} \;
Note, the -H is mac-specific, it shows the filename in the results.
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Specifying an Index (Non-Unique Key) Using JPA
...tHub. Java, Kotlin, Android): Annotation io.requery.Index;
Exposed (Kotlin SQL Library): org.jetbrains.exposed.sql.Index, org.jetbrains.exposed.sql.Table#index(). Example:
object Persons : IdTable() {
val code = varchar("code", 50).index()
}
= ORM for Android =
♥ ActiveAndroid: Annotat...
Only read selected columns
... fread("data.txt", select = c(1:7), data.table = FALSE)
2) With read.csv.sql from the sqldf-package:
Another alternative is the read.csv.sql function from the sqldf package:
library(sqldf)
dat <- read.csv.sql("data.txt",
sql = "select Year,Jan,Feb,Mar,Apr,May,Jun from file...