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Is there a REAL performance difference between INT and VARCHAR primary keys?
...performance difference between using INT vs. VARCHAR as a primary key in MySQL? I'd like to use VARCHAR as the primary key for reference lists (think US States, Country Codes) and a coworker won't budge on the INT AUTO_INCREMENT as a primary key for all tables.
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How to choose the id generation strategy when using JPA and Hibernate
...ble. Do not use in a cluster.
identity
supports identity columns in DB2, MySQL, MS SQL Server, Sybase and HypersonicSQL. The returned identifier is of type long, short or int.
sequence
uses a sequence in DB2, PostgreSQL, Oracle, SAP DB, McKoi or a generator in Interbase. The returned identifier is o...
Reference - What does this error mean in PHP?
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Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given
First and foremost:
Please, don't use mysql_* functions in new code. They are no longer maintained and are officially deprecated. See the red box? Learn...
ExecuteReader requires an open and available Connection. The connection's current state is Connectin
When attempting to connect to MSSQL database via ASP.NET online, I will get the following when two or more people connect simultaneously:
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“Incorrect string value” when trying to insert UTF-8 into MySQL via JDBC?
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MySQL's utf8 permits only the Unicode characters that can be represented with 3 bytes in UTF-8. Here you have a character that needs 4 bytes: \xF0\x90\x8D\x83 (U+10343 GOTHIC LETTER SAUIL).
If you have MySQL 5.5 or later you c...
When should I use a composite index?
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@felwithe MySQL can only use one index per each of the tables in a query (Exemptions are there. eg, Merging of indexes). Which ideally means that a table in a query, must use a single index for all where-clause, table join, group-by and ...
Insert, on duplicate update in PostgreSQL?
...m an answer on Stack Overflow how to perform multiple updates at once in MySQL using the following syntax:
16 Answers
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Storing Data in MySQL as JSON
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CouchDB and MySQL are two very different beasts. JSON is the native way to store stuff in CouchDB. In MySQL, the best you could do is store JSON data as text in a single field. This would entirely defeat the purpose of storing it in an RDB...
Does MySQL ignore null values on unique constraints?
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Yes, MySQL allows multiple NULLs in a column with a unique constraint.
CREATE TABLE table1 (x INT NULL UNIQUE);
INSERT table1 VALUES (1);
INSERT table1 VALUES (1); -- Duplicate entry '1' for key 'x'
INSERT table1 VALUES (NULL);
I...
How can I access the MySQL command line with XAMPP for Windows?
How can I access the MySQL command line with XAMPP for Windows?
15 Answers
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