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Fast way to discover the row count of a table in PostgreSQL
...in your case.
Instead of getting the exact count (slow with big tables):
SELECT count(*) AS exact_count FROM myschema.mytable;
You get a close estimate like this (extremely fast):
SELECT reltuples::bigint AS estimate FROM pg_class where relname='mytable';
How close the estimate is depends on ...
How to generate a range of numbers between two numbers?
...
Select non-persisted values with the VALUES keyword. Then use JOINs to generate lots and lots of combinations (can be extended to create hundreds of thousands of rows and beyond).
SELECT ones.n + 10*tens.n + 100*hundreds.n +...
SQL Server Insert if not exists
..., Assunto, Data)
VALUES (@_DE, @_ASSUNTO, @_DATA)
WHERE NOT EXISTS ( SELECT * FROM EmailsRecebidos
WHERE De = @_DE
AND Assunto = @_ASSUNTO
AND Data = @_DATA);
END
replace with
BEGIN
IF NOT EXISTS (SELECT * FROM EmailsRecebidos
...
How to get a date in YYYY-MM-DD format from a TSQL datetime field?
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SELECT CONVERT(char(10), GetDate(),126)
Limiting the size of the varchar chops of the hour portion that you don't want.
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Oracle Differences between NVL and Coalesce
...the first non-NULL (there are some exceptions, such as sequence NEXTVAL):
SELECT SUM(val)
FROM (
SELECT NVL(1, LENGTH(RAWTOHEX(SYS_GUID()))) AS val
FROM dual
CONNECT BY
level <= 10000
)
This runs for almost 0.5 seconds, since it generates...
What is the reason not to use select *?
...eople claim that you should specifically name each column you want in your select query.
20 Answers
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Check if a row exists, otherwise insert
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I assume a single row for each flight? If so:
IF EXISTS (SELECT * FROM Bookings WHERE FLightID = @Id)
BEGIN
--UPDATE HERE
END
ELSE
BEGIN
-- INSERT HERE
END
I assume what I said, as your way of doing things can overbook a flight, as it will insert a new row when there are 1...
What is the difference D3 datum vs. data?
...rs here on SO are not complete as they only cover the case when you invoke selection.data and selection.datum with an input data parameter. Even in that scenario, the two behave differently if the selection is a single element versus when it contains multiple elements. Moreover, both of these method...
Count number of records returned by group by
...
You can do both in one query using the OVER clause on another COUNT
select
count(*) RecordsPerGroup,
COUNT(*) OVER () AS TotalRecords
from temptable
group by column_1, column_2, column_3, column_4
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jQuery - select all text from a textarea
...can I make it so when you click inside a textarea, its entire content gets selected?
6 Answers
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