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How do you delete a column by name in data.table?
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Any of the following will remove column foo from the data.table df3:
# Method 1 (and preferred as it takes 0.00s even on a 20GB data.table)
df3[,foo:=NULL]
df3[, c("foo","bar"):=NULL] # remove two columns
myVar = "foo"
df3[, (myVar):=NULL] # lookup myVar contents
# Method 2a ...
ROW_NUMBER() in MySQL
... kind of isn't).
I often plump for a null-self-join:
SELECT t0.col3
FROM table AS t0
LEFT JOIN table AS t1 ON t0.col1=t1.col1 AND t0.col2=t1.col2 AND t1.col3>t0.col3
WHERE t1.col1 IS NULL;
“Get the rows in the table for which no other row with matching col1,col2 has a higher col3.” (You w...
How to get primary key column in Oracle?
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SELECT cols.table_name, cols.column_name, cols.position, cons.status, cons.owner
FROM all_constraints cons, all_cons_columns cols
WHERE cols.table_name = 'TABLE_NAME'
AND cons.constraint_type = 'P'
AND cons.constraint_name = cols.constra...
How to create materialized views in SQL Server?
...ually I want to create a view and it should update automatically when base tables are changed. Can anyone explain with an query example..
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INSERT INTO…SELECT for all MySQL columns
...The correct syntax is described in the manual. Try this:
INSERT INTO this_table_archive (col1, col2, ..., coln)
SELECT col1, col2, ..., coln
FROM this_table
WHERE entry_date < '2011-01-01 00:00:00';
If the id columns is an auto-increment column and you already have some data in both tables the...
How can I export tables to Excel from a webpage [closed]
How can I export tables to Excel from a webpage. I want the export to contain all the formatting and colours.
14 Answers
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How do I see what character set a MySQL database / table / column is?
... FROM information_schema.SCHEMATA
WHERE schema_name = "schemaname";
For Tables:
SELECT CCSA.character_set_name FROM information_schema.`TABLES` T,
information_schema.`COLLATION_CHARACTER_SET_APPLICABILITY` CCSA
WHERE CCSA.collation_name = T.table_collation
AND T.table_schema = "schemana...
How to set up fixed width for ?
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I was having the same issue, I made the table fixed and then specified my td width. If you have th you can do those as well.
table {
table-layout: fixed;
word-wrap: break-word;
}
Template:
<td style="width:10%">content</td>
Please use CSS ...
How can I alter a primary key constraint using SQL syntax?
I have a table that is missing a column in its primary key constraint. Instead of editing it through SQL Server, I want to put this in a script to add it as part of our update scripts.
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Why do Lua arrays(tables) start at 1 instead of 0?
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In Programming in Lua's first discussion of tables, they mention:
Since you can index a table with any value, you can start the indices of an array with any number that pleases you. However, it is customary in Lua to start arrays with 1 (and not with 0, as in C) an...