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Displaying posts with tag: varchar (reset)

Log Buffer #441: A Carnival of the Vanities for DBAs
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This Log Buffer Edition dives deep into the ocean of blogosphere and surfaces with some cool blog posts from Oracle, SQL Server and MySQL.


  • Lets Talk DB Perth
  • The Fundamental Challenge of Computer System Performance
  • Index Advanced Compression: Multi-Column …
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Understanding MySQL binary and non-binary string data types
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Having reviewed different table structures designed by different people, I have come to the conclusion that binary and non-binary string data types are used without consideration of the consequences of choosing either one. The confusion stems from the fact that both non-binary and binary string data appear to store characters because they can be saved as quoted string.

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On first glance, it looks like TEXT and VARCHAR can store the same information. However, there are fundamental differences between the way TEXT fields and VARCHAR fields work, which are important to take into consideration.

VARCHAR is actually part of the ISO SQL:2003 standard; The TEXT data types, including TINYTEXT, are non-standard.

TEXT data types are stored as separate objects from the tables and result sets that contain them. This storage is transparent — there is no difference in how a query involving a TEXT field is written versus one involving a VARCHAR field. Since TEXT is not stored …

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The maximum length of a VARCHAR is only restricted by the maximum row length. In most storage engines, the maximum row length is the maximum allowed by MySQL, which is 65,535 bytes. Only the NDB storage engine has a different maximum value.

The VARCHAR data type has some overhead. If the length of VARCHAR is less than 255, one byte per row is used to store the actual length of the string. If the length of VARCHAR is greater than 255, the overhead cost of storing the string length is two bytes per row. Thus, the maximum length of a VARCHAR should be 65,533 bytes.

However, that is not the case:

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Showing entries 1 to 4

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