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Best way to test if a row exists in a MySQL table
I'm trying to find out if a row exists in a table. Using MySQL, is it better to do a query like this:
12 Answers
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Insert into … values ( SELECT … FROM … )
I am trying to INSERT INTO a table using the input from another table. Although this is entirely feasible for many database engines, I always seem to struggle to remember the correct syntax for the SQL engine of the day ( MySQL , Oracle , SQL Server , Informix , and DB2 ).
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How do I create some kind of table of content in GitHub wiki?
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It is nicely demonstrated in the Table of Contents of the Markdown Cheatsheet.
##### Table of Contents
[Headers](#headers)
[Emphasis](#emphasis)
...snip...
<a name="headers"/>
## Headers
If you hover over a Header in a GitHub Markdown file...
Foreign Key naming scheme
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The standard convention in SQL Server is:
FK_ForeignKeyTable_PrimaryKeyTable
So, for example, the key between notes and tasks would be:
FK_note_task
And the key between tasks and users would be:
FK_task_user
This gives you an 'at a glance' view of which tables are involve...
Android: upgrading DB version and adding new table
I've already created sqlite tables for my app, but now I want to add a new table to the database.
5 Answers
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MySQL, update multiple tables with one query
I have a function that updates three tables, but I use three queries to perform this. I wish to use a more convenient approach for good practice.
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How can a LEFT OUTER JOIN return more records than exist in the left table?
I have a very basic LEFT OUTER JOIN to return all results from the left table and some additional information from a much bigger table. The left table contains 4935 records yet when I LEFT OUTER JOIN it to an additional table the record count is significantly larger.
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Importing a CSV file into a sqlite3 database table using Python
...nge to 'sqlite:///your_filename.db'
cur = con.cursor()
cur.execute("CREATE TABLE t (col1, col2);") # use your column names here
with open('data.csv','r') as fin: # `with` statement available in 2.5+
# csv.DictReader uses first line in file for column headings by default
dr = csv.DictReader(...
How to import multiple .csv files at once?
...r answers using things like do.call(rbind,...), dplyr::bind_rows() or data.table::rbindlist().
If you really want each data frame in a separate object, even though that's often inadvisable, you could do the following with assign:
temp = list.files(pattern="*.csv")
for (i in 1:length(temp)) assign(...
Adding a new value to an existing ENUM Type
I have a table column that uses an enum type. I wish to update that enum type to have an additional possible value. I don't want to delete any existing values, just add the new value. What is the simplest way to do this?
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