大约有 3,630 项符合查询结果（耗时：0.0118秒） [XML]
Rails: select unique values from a column
...iq.pluck(:rating) is the most efficient way of doing this - this generates SQL which use SELECT DISTINCT rather than applying .uniq to an array
– Mikey
Jun 19 '13 at 15:38
25
...
“INSERT IGNORE” vs “INSERT … ON DUPLICATE KEY UPDATE”
...ut the values you insert don't map to a partition.
If you use REPLACE, MySQL actually does a DELETE followed by an INSERT internally, which has some unexpected side effects:
A new auto-increment ID is allocated.
Dependent rows with foreign keys may be deleted (if you use cascading foreign keys...
Handling warning for possible multiple enumeration of IEnumerable
...oom for too many assumptions. Do you really want someone to pass a LINQ to SQL query to this method, only for you to enumerate it twice (getting potentially different results each time?)
The semantic missing here is that a caller, who perhaps doesn't take time to read the details of the method, may...
How to move columns in a MySQL table?
Currently I am having the following MySQL table: Employees (empID, empName, department);
4 Answers
...
How to subtract 30 days from the current datetime in mysql?
How do I subtract 30 days from the current datetime in mysql?
8 Answers
8
...
How to map calculated properties with JPA and Hibernate
...ntioned, @Formula is perfect for this when using Hibernate. You can use an SQL fragment:
@Formula("PRICE*1.155")
private float finalPrice;
Or even complex queries on other tables:
@Formula("(select min(o.creation_date) from Orders o where o.customer_id = id)")
private Date firstOrderDate;
Wher...
JSON encode MySQL results
How do I use the json_encode() function with MySQL query results? Do I need to iterate through the rows or can I just apply it to the entire results object?
...
'IF' in 'SELECT' statement - choose output value based on column values
...(type = 'P', amount, amount * -1) as amount
FROM report
See http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html.
Additionally, you could handle when the condition is null. In the case of a null amount:
SELECT id,
IF(type = 'P', IFNULL(amount,0), IFNULL(amount,0) * -1) as a...
find() with nil when there are no records
...hen you pass a hash as 'x' to Something.find_by(id: x) it would create a SQL statement with all the attribute/value pairs of the hash as part of the WHERE clause. Looks like a Rails bug to me.
– Tilo
May 24 '17 at 21:44
...
Dropping Unique constraint from MySQL table
How can I drop the "Unique Key Constraint" on a column of a MySQL table using phpMyAdmin?
10 Answers
...