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How do I modify a MySQL column to allow NULL?
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You want the following:
ALTER TABLE mytable MODIFY mycolumn VARCHAR(255);
Columns are nullable by default. As long as the column is not declared UNIQUE or NOT NULL, there shouldn't be any problems.
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Caching a jquery ajax response in javascript/browser
...onsole for debugging.
You can clear the cache on any given page via
jSQL.tables = {}; jSQL.persist();
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Why malloc+memset is slower than calloc?
...n parts here: your program, the standard library, the kernel, and the page tables. You already know your program, so...
Memory allocators like malloc() and calloc() are mostly there to take small allocations (anything from 1 byte to 100s of KB) and group them into larger pools of memory. For exam...
What's wrong with foreign keys?
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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...
Numbering rows within groups in a data frame
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Use ave, ddply, dplyr or data.table:
df$num <- ave(df$val, df$cat, FUN = seq_along)
or:
library(plyr)
ddply(df, .(cat), mutate, id = seq_along(val))
or:
library(dplyr)
df %>% group_by(cat) %>% mutate(id = row_number())
or (the most memor...
Adding iOS UITableView HeaderView (not section header)
I want to add a table header (not section headers) like in the contacts app for example:
5 Answers
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How do I find a specific table in my EDMX model quickly?
I was wondering if anyone knows a quicker way to find a table in the EDMX model than just scrolling through the diagram and looking for the thing. Our database has around 50 tables in it and when I'm looking for a specific one it's just a chore to see where VS put the thing.
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Specifying column name in a “references” migration
I want to make a migration in Rails, referencing another table. Usually, I would do something like:
6 Answers
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Force R not to use exponential notation (e.g. e+10)?
...file auto-executes it. This is useful for e.g. default package loads, data.table configuration, environment etc. Again, that config can run to a page of settings, and there's zero chance you'll remember those and their syntax and type them in
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String literals and escape characters in postgresql
Attempting to insert an escape character into a table results in a warning.
5 Answers
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