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Why does PostgreSQL perform sequential scan on indexed column?
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If the SELECT returns more than approximately 5-10% of all rows in the table, a sequential scan is much faster than an index scan.
This is because an index scan requires several IO operations for each row (look up the row in the ...
Tablix: Repeat header rows on each page not working - Report Builder 3.0
...the Groupings pane. (Click the arrow to the right of the Column Groups and select Advanced Mode.)
In the Row Groups area (not Column Groups), click on a Static group, which highlights the corresponding textbox in the tablix. Click through each Static group until it highlights the leftmost column...
How do I connect to a MySQL Database in Python?
...ueries you need
cur = db.cursor()
# Use all the SQL you like
cur.execute("SELECT * FROM YOUR_TABLE_NAME")
# print all the first cell of all the rows
for row in cur.fetchall():
print row[0]
db.close()
Of course, there are thousand of possibilities and options; this is a very basic example. Y...
How to find Unused Amazon EC2 Security groups
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If you select all of your security groups in the EC2 console, then press actions -> Delete Security Groups, a popup will appear telling you that you cannot delete security groups that are attached to instances, other security gro...
Export from sqlite to csv using shell script
...qlite3
You have a separate call to sqlite3 for each line; by the time your select runs, your .out out.csv has been forgotten.
Try:
#!/bin/bash
./bin/sqlite3 ./sys/xserve_sqlite.db <<!
.headers on
.mode csv
.output out.csv
select * from eS1100_sensor_results;
!
instead.
sh/bash methods
You can...
What's the best way to make a d3.js visualisation layout responsive?
...n the window resizes like so:
var aspect = width / height,
chart = d3.select('#chart');
d3.select(window)
.on("resize", function() {
var targetWidth = chart.node().getBoundingClientRect().width;
chart.attr("width", targetWidth);
chart.attr("height", targetWidth / aspect);
});
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List tables in a PostgreSQL schema
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You can select the tables from information_schema
SELECT * FROM information_schema.tables
WHERE table_schema = 'public'
share
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How do I remove the first characters of a specific column in a table?
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SELECT RIGHT(MyColumn, LEN(MyColumn) - 4) AS MyTrimmedColumn
Edit:
To explain, RIGHT takes 2 arguments - the string (or column) to operate on, and the number of characters to return (starting at the "right" side of the stri...
Force Intellij IDEA to reread all maven dependencies
...le project and I do this. Does this command apply to all modules, just the selected one, or the first one in the project when it runs?
– slartibartfast
Sep 25 '15 at 22:06
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How many database indexes is too many?
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It depends on the operations that occur on the table.
If there's lots of SELECTs and very few changes, index all you like.... these will (potentially) speed the SELECT statements up.
If the table is heavily hit by UPDATEs, INSERTs + DELETEs ... these will be very slow with lots of indexes since t...