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Error 1046 No database Selected, how to resolve?
...ation.
If you're trying to do this via MySQL Workbench...
...you need to select the appropriate database/catalog in the drop down menu found above the :Object Browser: tab. You can specify the default schema/database/catalog for the connection - click the "Manage Connections" options under the SQL...
Oracle: If Table Exists
...
declare
c int;
begin
select count(*) into c from user_tables where table_name = upper('table_name');
if c = 1 then
execute immediate 'drop table table_name';
end if;
end;
That's for checking whether a table in the current schema exi...
Count table rows
...
SELECT COUNT(*) FROM fooTable;
will count the number of rows in the table.
See the reference manual.
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What makes a SQL statement sargable?
...non-sargable is to include a field inside a function in the where clause:
SELECT ... FROM ...
WHERE Year(myDate) = 2008
The SQL optimizer can't use an index on myDate, even if one exists. It will literally have to evaluate this function for every row of the table. Much better to use:
WHERE myDat...
Why do we always prefer using parameters in SQL statements?
I am very new to working with databases. Now I can write SELECT , UPDATE , DELETE , and INSERT commands. But I have seen many forums where we prefer to write:
...
Cannot ping AWS EC2 instance
...ICMP rule
Protocol: Echo Request
Port: N/A
Source: your choice (I would select Anywhere to be able to ping from any machine)
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What's the difference between RANK() and DENSE_RANK() functions in oracle?
...s a simple test script you can play with to see what happens:
with q as (
select 10 deptno, 'rrr' empname, 10000.00 sal from dual union all
select 11, 'nnn', 20000.00 from dual union all
select 11, 'mmm', 5000.00 from dual union all
select 12, 'kkk', 30000 from dual union all
select 10, 'fff', 4000...
MySQL Data - Best way to implement paging?
...e LIMIT clause can be used to constrain the number of rows returned by the SELECT statement. LIMIT takes one or two numeric arguments, which must both be nonnegative integer constants (except when using prepared statements).
With two arguments, the first argument specifies the offset of the first ro...
MySQL Error 1093 - Can't specify target table for update in FROM clause
...s question
In MySQL, you can't modify the same table which you use in the SELECT part.
This behaviour is documented at:
http://dev.mysql.com/doc/refman/5.6/en/update.html
Maybe you can just join the table to itself
If the logic is simple enough to re-shape the query, lose the subquery and join th...
What must I know to use GNU Screen properly? [closed]
... target window. Warning: it will let you know if anything changes.
Want to select window 15 directly? Try these in your .screenrc file:
bind ! select 11
bind @ select 12
bind \# select 13
bind $ select 14
bind % select 15
bind \^ select 16
bind & select 17
bind * select 18
bind ( selec...