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What is SELF JOIN and when would you use it? [duplicate]
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SQL self-join simply is a normal join which is used to join a table to itself.
Example:
Select *
FROM Table t1, Table t2
WHERE t1.Id = t2.ID
share...
MySQL Workbench: How to keep the connection alive
Error Code: 2013. Lost connection to MySQL server during query
9 Answers
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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
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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...
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
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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?
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'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
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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
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Extracting the last n characters from a string in R
...n I get the last n characters from a string in R?
Is there a function like SQL's RIGHT?
15 Answers
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