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SQL: How to properly check if a record exists
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It's better to use either of the following:
-- Method 1.
SELECT 1
FROM table_name
WHERE unique_key = value;
-- Method 2.
SELECT COUNT(1)
FROM table_name
WHERE unique_key = value;
The first alternative should give you no result or one result, the second count should be zero or on...
Why can't I use an alias in a DELETE statement?
... I was mainly just curious, because I normally use aliases when using SELECT and other such statements, so I instinctively did what I'm used to and was wondering why it didn't work properly.
– Ricardo Altamirano
Jun 12 '12 at 21:38
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What does a type followed by _t (underscore-t) represent?
... could cause some confusion. As well as size_t, the C89 standard defines wchar_t, off_t, ptrdiff_t, and probably some others I've forgotten. The C99 standard defines a lot of extra types, such as uintptr_t, intmax_t, int8_t, uint_least16_t, uint_fast32_t, and so on. These new types are formally d...
Copy data into another table
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If both tables are truly the same schema:
INSERT INTO newTable
SELECT * FROM oldTable
Otherwise, you'll have to specify the column names (the column list for newTable is optional if you are specifying a value for all columns and selecting columns in the same order as newTable's schema)...
How to deal with SQL column names that look like SQL keywords?
...ange the name because I didn't make it.
Am I allowed to do something like SELECT from FROM TableName or is there a special syntax to avoid the SQL Server being confused?
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How can I echo HTML in PHP?
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@MhdSyrwan just random chars, you can read more here php.net/manual/en/…
– lfx
Sep 23 '11 at 18:22
1
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Why do you need to create a cursor when querying a sqlite database?
...les traversal over the records in a database". For example c.execute('''SELECT * FROM users''') returns an iterator that you can call fetchall() on (or another cursor method). Some SQL queries return empty iterators, but that should be expected, not surprising.
– Powers
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Select mySQL based only on month and year
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SELECT * FROM projects WHERE YEAR(Date) = 2011 AND MONTH(Date) = 5
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Consistency of hashCode() on a Java string
....x the hashCode
function for long Strings worked by
sampling every nth character. This
pretty well guaranteed you would have
many Strings hashing to the same
value, thus slowing down Hashtable
lookup. In JDK 1.2 the function has
been improved to multiply the result
so far by 31 then ...
How do I find numeric columns in Pandas?
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You could use select_dtypes method of DataFrame. It includes two parameters include and exclude. So isNumeric would look like:
numerics = ['int16', 'int32', 'int64', 'float16', 'float32', 'float64']
newdf = df.select_dtypes(include=numer...