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What's the difference between NOT EXISTS vs. NOT IN vs. LEFT JOIN WHERE IS NULL?
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Another point is that if table1 .a contains NULL the EXISTS query will not return this row but the NOT IN query will if table2 is empty. NOT IN vs. NOT EXISTS Nullable Columns: SQL Server
– Martin Smith
Jun 19 '...
Vertically align text next to an image?
...lt;/div>
Multiple-lines vertical-align:middle
<div style="display:table;width:30px;height:60px;">
<div style="display:table-cell;height:30px;">This is positioned in the middle</div>
</div>
If you must support ancient versions of IE <= 7
In order to get this to w...
Throw an error in a MySQL trigger
If I have a trigger before the update on a table, how can I throw an error that prevents the update on that table?
7 An...
Is there any boolean type in Oracle databases?
...efer char(1) because it uses less space. You can check it this way: create table testbool (boolc char(1), booln number(1)); insert into testbool values ('Y', 1 ); select dump(boolc), dump(booln) from testbool; That CHAR is stored: Typ=96 Len=1: 89 and that NUMBER: Typ=2 Len=2: 193,2 At least in 12c...
SET versus SELECT when assigning variables?
... @var varchar(20)
set @var = 'Joe'
set @var = (select name from master.sys.tables where name = 'qwerty')
select @var /* @var is now NULL */
set @var = 'Joe'
select @var = name from master.sys.tables where name = 'qwerty'
select @var /* @var is still equal to 'Joe' */
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Generate GUID in MySQL for existing Data?
I've just imported a bunch of data to a MySQL table and I have a column "GUID" that I want to basically fill down all existing rows with new and unique random GUID's.
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How to export table as CSV with headings on Postgresql?
I'm trying to export a PostgreSQL table with headings to a CSV file via command line, however I get it to export to CSV file, but without headings.
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Using CSS td width absolute, position
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This may not be what you want to hear, but display: table-cell does not respect width and will be collapsed based on the width of the entire table. You can get around this easily just by having a display: block element inside of the table cell itself whose width you specify, ...
How do HashTables deal with collisions?
I've heard in my degree classes that a HashTable will place a new entry into the 'next available' bucket if the new Key entry collides with another.
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Difference between Key, Primary Key, Unique Key and Index in MySQL
...on columns used in JOIN, WHERE, and ORDER BY clauses.
Imagine you have a table called users and you want to search for all the users which have the last name 'Smith'. Without an index, the database would have to go through all the records of the table: this is slow, because the more records you ha...