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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 '...
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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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...
How to get size of mysql database?
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Run this query and you'll probably get what you're looking for:
SELECT table_schema "DB Name",
ROUND(SUM(data_length + index_length) / 1024 / 1024, 1) "DB Size in MB"
FROM information_schema.tables
GROUP BY table_schema;
This query comes from the mysql forums, where there are more c...
How can prepared statements protect from SQL injection attacks?
...SELECT * FROM users where id=1
while this code
$spoiled_data = "1; DROP TABLE users;"
$query = "SELECT * FROM users where id=$spoiled_data";
will produce a malicious sequence
SELECT * FROM users where id=1; DROP TABLE users;
It works because we are adding the data directly to the prog...
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...
How to store arrays in MySQL?
I have two tables in MySQL. Table Person has the following columns:
7 Answers
7
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What requests do browsers' “F5” and “Ctrl + F5” refreshes generate?
...trol by adding "Pragma: No-cache" when you pressed CTRL-F5.
Edit: Updated table
The table below is updated with information on what will happen when the browser's refresh-button is clicked (after a request by Joel Coehoorn), and the "max-age=0" Cache-control-header.
Updated table, 27 September 20...
What is the difference between a schema and a table and a database?
...bably a n00blike (or worse) question. But I've always viewed a schema as a table definition in a database. This is wrong or not entirely correct. I don't remember much from my database courses.
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