大约有 36,200 项符合查询结果（耗时：0.0293秒） [XML]
find vs find_by vs where
... suits your needs best.
The find method is usually used to retrieve a row by ID:
Model.find(1)
It's worth noting that find will throw an exception if the item is not found by the attribute that you supply. Use where (as described below, which will return an empty array if the attribute is not f...
Are PHP Variables passed by value or by reference?
Are PHP variables passed by value or by reference?
14 Answers
14
...
SQL - using alias in Group By
...uery was executed in the following order:
FROM clause
WHERE clause
GROUP BY clause
HAVING clause
SELECT clause
ORDER BY clause
For most relational database systems, this order explains which names (columns or aliases) are valid because they must have been introduced in a previous step.
So in Or...
JavaScript by reference vs. by value [duplicate]
...me good comprehensive reading material on when JavaScript passes something by value and when by reference and when modifying a passed item affects the value outside a function and when not. I'm also interested in when assigning to another variable is by reference vs. by value and whether that follo...
ORA-00979 not a group by expression
...
You must put all columns of the SELECT in the GROUP BY or use functions on them which compress the results to a single value (like MIN, MAX or SUM).
A simple example to understand why this happens: Imagine you have a database like this:
FOO BAR
0 A
0 B
and you run SELE...
How to group time by hour or by 10 minutes
...
finally done with
GROUP BY
DATEPART(YEAR, DT.[Date]),
DATEPART(MONTH, DT.[Date]),
DATEPART(DAY, DT.[Date]),
DATEPART(HOUR, DT.[Date]),
(DATEPART(MINUTE, DT.[Date]) / 10)
sh...
The SQL OVER() clause - when and why is it useful?
...d why I need it.
What does the function Over do? What does Partitioning By do?
Why can't I make a query with writing Group By SalesOrderID ?
...
Is there any difference between GROUP BY and DISTINCT
...ed; the SQL Server is smart enough to realize that if you are using "Group By" and not using any aggregate functions, then what you actually mean is "Distinct" - and therefore it generates an execution plan as if you'd simply used "Distinct."
However, I think it's important to note Hank's response ...
Passing by reference in C
If C does not support passing a variable by reference, why does this work?
17 Answers
...
SQL Query to concatenate column values from multiple rows in Oracle
...one is to use LISTAGG:
SELECT pid, LISTAGG(Desc, ' ') WITHIN GROUP (ORDER BY seq) AS description
FROM B GROUP BY pid;
Then join to A to pick out the pids you want.
Note: Out of the box, LISTAGG only works correctly with VARCHAR2 columns.
...