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How many records can be possible & how many maximum records can be effective in mysql?
Actually my table has
24 Tables
1000000 Rows in Table (Each table (max))
Can I use mysql, please help me to solve my problem.
Yes you can use mysql perfectly.
One million rows (AKA records) is not too much for mysql, if you index that.
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I am trying to join an old sql table with a new one but exclude the duplicate entries, this needs to be in a delphi program as well, and im a noob at that, any ideas?
These both keywords will make your data to combine and display in a single column.
Union - Removes the duplicate entries of the table
Union All - Includes the duplicate entries
It would be better if you provide an example with input and output, that would clarify your question the most.
you can use the union all operator instead of the union operator for joining two tables that not remove duplicates from the table.
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Im curious what is the distinct use of pivot table in database? I mean, how is it apply in real life.
Pivot query help us to generate an interactive table that quickly combines and compares large amounts of data. We can rotate its rows and columns to see different summaries of the source data, and we can display the details for areas of interest at a glance. It also help us to generate Multidimensional reporting.
for more information visit:
http://www.codeproject.com/Tips/500811/Simple-Way-To-Use-Pivot-In-SQL-Query
https://technet.microsoft.com/en-us/library/ms177410(v=sql.105).aspx
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Consider two queries,
Select * from table where size = 'L';
Select * from table where id IN (691,12,123,5123,....); # id is primary key for the table. and covers all the cases for which size ='L'.
Now consider a table which has 2 million records and i'll be firing both the queries.
Which of the two queries will run faster and why?
Consider this situation in terms of a system which filters out data on select of the option.
In Short: Ths answer depends on how many rows have size='L'. If there are many rows the the second will be more efficient because an index on size ist slow (cardinality).
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This is more of a theoretical question. Suppose we have a MySQL DB with n number of tables. Out of these m tables are possible to join (n-m tables cannot be joined on a key or won't even make any sense to join them). Given this; is there a finite number of MySQL queries possible for this DB and if so, how do we determine that number?
SQL is a constructive grammar and therefore has an limitless number of queries.
It doesn't matter how many tables are involved.
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I have several databases represents the companies we work.
In every database there are fields which we work on.
And in the fields area, there are field infos and our engineer who worked at that field.
I need to search all databases and filter with engineer names, to get a list of fields he worked.
I hope I could explain.
Any simple solution?
Nope. You're going to have to manually write queries to search each table in each database. The whole idea of database schemas and tables is that they are distinct wrappers for data, which can't be implicitly joined.