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How to find Unused Amazon EC2 Security groups
...
If you select all of your security groups in the EC2 console, then press actions -> Delete Security Groups, a popup will appear telling you that you cannot delete security groups that are attached to instances, other security gro...
How can I get the intersection, union, and subset of arrays in Ruby?
...et operations on arrays by doing &(intersection), -(difference), and |(union).
Obviously I didn't implement the MultiSet to spec, but this should get you started:
class MultiSet
attr_accessor :set
def initialize(set)
@set = set
end
# intersection
def &(other)
@set & o...
SQL: deleting tables with prefix
...r you:
In the MySQL shell or through PHPMyAdmin, use the following query
SELECT CONCAT( 'DROP TABLE ', GROUP_CONCAT(table_name) , ';' )
AS statement FROM information_schema.tables
WHERE table_name LIKE 'myprefix_%';
This will generate a DROP statement which you can than copy and execut...
Difference between CTE and SubQuery?
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CTE's are most useful for recursion:
WITH hier(cnt) AS (
SELECT 1
UNION ALL
SELECT cnt + 1
FROM hier
WHERE cnt < @n
)
SELECT cnt
FROM hier
will return @n rows (up to 101). Useful for calendars, dummy rowsets etc.
They are als...
In MySQL, can I copy one row to insert into the same table?
...e) but I want to do this without having to list all the columns after the "select", because this table has too many columns.
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MySQL Error 1153 - Got a packet bigger than 'max_allowed_packet' bytes
I'm importing a MySQL dump and getting the following error.
14 Answers
14
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MySQL: How to copy rows, but change a few fields?
...able
( Event_ID
, col2
...
)
SELECT "155"
, col2
...
FROM Table WHERE Event_ID = "120"
Here, the col2, ... represent the remaining columns (the ones other than Event_ID) in your table.
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Troubleshooting “Illegal mix of collations” error in mysql
Am getting the below error when trying to do a select through a stored procedure in MySQL.
16 Answers
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MySQL OPTIMIZE all tables?
...>.<your_table>;, optimize all tables in a given schema like this: select concat('OPTIMIZE NO_WRITE_TO_BINLOG TABLE ',table_schema,'.',table_name,';') into outfile '/tmp/optimize_all_tables.sql' from information_schema.tables where table_schema = 'pabeta' and table_type = 'base table'; sourc...
MySQL indexes - what are the best practices?
...t them. Generally I put an index on any fields that I will be searching or selecting using a WHERE clause but sometimes it doesn't seem so black and white.
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