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Find rows with multiple duplicate fields with Active Record, Rails & Postgres
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Tested & Working Version
User.select(:first,:email).group(:first,:email).having("count(*) > 1")
Also, this is a little unrelated but handy. If you want to see how times each combination was found, put .size at the end:
User.select(:first,:email).gro...
MySQL: Selecting multiple fields into multiple variables in a stored procedure
Can I SELECT multiple columns into multiple variables within the same select query in MySQL?
3 Answers
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LINQ Using Max() to select a single row
I'm using LINQ on an IQueryable returned from NHibernate and I need to select the row with the maximum value(s) in a couple of fields.
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Select the values of one property on all objects of an array in PowerShell
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I think you might be able to use the ExpandProperty parameter of Select-Object.
For example, to get the list of the current directory and just have the Name property displayed, one would do the following:
ls | select -Property Name
This is still returning DirectoryInfo or FileInfo obje...
How to check if a file is a valid image file?
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A lot of times the first couple chars will be a magic number for various file formats. You could check for this in addition to your exception checking above.
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how to emulate “insert ignore” and “on duplicate key update” (sql merge) with postgresql?
... two queries, one for INSERT and one for UPDATE (as an appropriate join/subselect of course - no need to write your main filter twice)
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Meaning of $? (dollar question mark) in shell scripts
...k() == 0) {
/* Call false. */
execl("./false", "./false", (char *)NULL);
}
int status;
/* Wait for a child to finish. */
wait(&status);
/* Status encodes multiple fields,
* we need WEXITSTATUS to get the exit status:
* http://stackoverflow.com/questi...
How can I select the first day of a month in SQL?
I just need to select the first day of the month of a given datetime variable.
30 Answers
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What is the worst real-world macros/pre-processor abuse you've ever come across?
...efine static
#define void int
#define main(x) main()
struct F{void println(char* s){std::cout << s << std::endl;}};
struct S{F out;};
public static void main(String[] args) {
System.out.println("Hello World!");
}
Challenge: Can anyone do it with fewer defines and structs? ;-)
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How to select all records from one table that do not exist in another table?
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SELECT t1.name
FROM table1 t1
LEFT JOIN table2 t2 ON t2.name = t1.name
WHERE t2.name IS NULL
Q: What is happening here?
A: Conceptually, we select all rows from table1 and for each row we attempt to find a row in table2 wi...