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Does a UNIQUE constraint automatically create an INDEX on the field(s)?
...email, user_id) is enough, you don't need a separate index on email only - MySQL can use leftmost parts of a composite index. There may be some border cases where the size of an index can slow down your queries, but you should not worry about them until you actually run into them.
As for testing in...
Does Foreign Key improve query performance?
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foreign keys do improve performance, at least in MySQL. Moreover, you're right, the creation of a FK does not create an index; the creation of a FK requires an index
– Félix Gagnon-Grenier
Aug 26 '14 at 17:31
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Database Structure for Tree Data Structure
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Have a look at Managing Hierarchical Data in MySQL. It discusses two approaches for storing and managing hierarchical (tree-like) data in a relational database.
The first approach is the adjacency list model, which is what you essentially describe: having a foreign key...
Update all values of a column to lowercase
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See http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_lower
UPDATE table_name SET tag = LOWER(tag)
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How to host a Node.Js application in shared hosting [closed]
... 30 minutes to set up the configuration, and it'll work with npm, Express, MySQL, etc.
See a2hosting.com.
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Why should I capitalize my SQL keywords? [duplicate]
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So does MySQL, and for good and for bad (mostly bad:-), many developers first exposure to SQL is through MySQL.
– Paul Tomblin
Mar 4 '09 at 13:41
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Sqlite LIMIT / OFFSET query
...T <count> OFFSET <skip>
It's compatible with the syntax from MySQL and PostgreSQL. MySQL supports both syntax forms, and its docs claim that the second syntax with OFFSET was meant to provide compatibility with PostgreSQL. PostgreSQL docs show it only supports the second syntax, and ...
String concatenation does not work in SQLite
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Oracle CONCAT(string1, string2) or ||
MySQL CONCAT(string1, string2, string3...) or || if PIPES_AS_CONCAT enabled
Postgres CONCAT(string1, string2, string3...) or ||
Microsoft SQL Server 2012+ CONCAT(string1, string2, str...
Can someone explain in simple terms to me what a directed acyclic graph is?
... Andriyev, +1 for the deadlock example. This is in fact used by MySQL's InnoDB engine, and they call it a "wait-for-graph", as in, "that row has to wait for the lock on that row to be released"
– Roland Bouman
Feb 17 '10 at 19:40
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How to do an update + join in PostgreSQL?
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coming from mysql it's unintuitive that the same join used for select won't also update just by adding a set phrase :( still - the syntax for this is probably easier for a newcomer to sql to master.
– WEBjuju
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