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SQL join: selecting the last records in a one-to-many relationship
Suppose I have a table of customers and a table of purchases. Each purchase belongs to one customer. I want to get a list of all customers along with their last purchase in one SELECT statement. What is the best practice? Any advice on building indexes?
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How to place div side by side
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Using CSS display property - which can be used to make divs act like a table:
<div style="width: 100%; display: table;">
<div style="display: table-row">
<div style="width: 600px; display: table-cell;"> Left </div>
<div style="display: table-ce...
Update all values of a column to lowercase
...v.mysql.com/doc/refman/5.0/en/string-functions.html#function_lower
UPDATE table_name SET tag = LOWER(tag)
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What's wrong with foreign keys?
...s
you can get nice "on delete cascade" behavior, automatically cleaning up tables
knowing about the relationships between tables in the database helps the Optimizer plan your queries for most efficient execution, since it is able to get better estimates on join cardinality.
FKs give a pretty big hi...
Transaction count after EXECUTE indicates a mismatching number of BEGIN and COMMIT statements. Previ
I have an Insert stored procedure which will feed data to Table1 and get the Column1 value from Table1 and call the second stored procedure which will feed the Table2.
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Split column at delimiter in data frame [duplicate]
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Essentially, it's a fancy convenience wrapper for using read.table(text = some_character_vector, sep = some_sep) and binding that output to the original data.frame. In other words, another A base R approach could be:
df <- data.frame(ID=11:13, FOO=c('a|b','b|c','x|y'))
cbind(df, re...
Add a reference column migration in Rails 4
A user has many uploads. I want to add a column to the uploads table that references the user . What should the migration look like?
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What are the underlying data structures used for Redis?
...e implemented with linked lists.
Sets and Hashes are implemented with hash tables.
Sorted sets are implemented with skip lists (a peculiar type of balanced trees).
But when lists, sets, and sorted sets are small in number of items and size of the largest values, a different, much more compact enco...
I want to use CASE statement to update some records in sql server 2005
...rk for the purpose but the else condition scan through every record in the table. Is there any way I can leave the unaffected rows as they are?
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Get properties and values from unknown object
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Here's something I use to transform an IEnumerable<T> into a DataTable that contains columns representing T's properties, with one row for each item in the IEnumerable:
public static DataTable ToDataTable<T>(IEnumerable<T> items)
{
var table = CreateDataTableForPropertiesO...