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What are the uses for Cross Join?
...t
size,
color
from
sizes CROSS JOIN colors
Maybe you want a table that contains a row for every minute in the day, and you want to use it to verify that a procedure has executed each minute, so you might cross three tables:
select
hour,
minute
from
hours CROSS JOIN minute...
Python SQL query string formatting
...Code Sample:
sql = ("SELECT field1, field2, field3, field4 "
"FROM table "
"WHERE condition1=1 "
"AND condition2=2;")
Works as well with f-strings:
fields = "field1, field2, field3, field4"
table = "table"
conditions = "condition1=1 AND condition2=2"
sql = (f"SELECT {fields...
Long press on UITableView
I would like to handle a long press on a UITableViewCell to print a "quick access menu".
Did someone already do this?
10...
How do I modify a MySQL column to allow NULL?
...
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.
...
How to Store Historical Data
...y to store historical data. Currently, for some systems, I use a separate table to store historical data, and I keep an original table for the current, active record. So, let's say I have table FOO. Under my system, all active records will go in FOO, and all historical records will go in FOO_Hist...
Simple way to copy or clone a DataRow?
...
You can use ImportRow method to copy Row from DataTable to DataTable with the same schema:
var row = SourceTable.Rows[RowNum];
DestinationTable.ImportRow(row);
Update:
With your new Edit, I believe:
var desRow = dataTable.NewRow();
var sourceRow = dataTable.Rows[rowNum]...
Fastest way to determine if record exists
...e fastest way with the least overhead to determine if a record exists in a table or not.
11 Answers
...
How to update column with null value
...
No special syntax:
CREATE TABLE your_table (some_id int, your_column varchar(100));
INSERT INTO your_table VALUES (1, 'Hello');
UPDATE your_table
SET your_column = NULL
WHERE some_id = 1;
SELECT * FROM your_table WHERE your_column IS NULL;
+---...
Convert a list of data frames into one data frame
... but in about Sep 2011 a new function rbindlist was introduced in the data.table package version 1.8.2, with a remark that "This does the same as do.call("rbind",l), but much faster". How much faster?
library(rbenchmark)
benchmark(
do.call = do.call("rbind", listOfDataFrames),
plyr_rbind.fill ...
How to add border radius on table row
...
You can only apply border-radius to td, not tr or table. I've gotten around this for rounded corner tables by using these styles:
table { border-collapse: separate; }
td { border: solid 1px #000; }
tr:first-child td:first-child { border-top-left-radius: 10px; }
tr:first-ch...