About wildcards and data type precedence

Implicit conversions in SQL Server follow a specific, predictable order, called data type precedence. This means that if you compare or add/concatenate two values, a and b, with different data types, you can predict which one will be implicitly converted to the data type of the other one in order to be able to complete the operation.

I stumbled on an interesting exception to this rule the other day.

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Collations and case sensitive wildcards

The other day, I ran across the following issue: I was looking to split a value using upper case and lower case characters. Here’s an example query:

SELECT PATINDEX('%[a-z][A-Z]%',
    'testValue' COLLATE Finnish_Swedish_CS_AS) AS offset

I expected this query to return the value 4, because at that offset in the string, there is a lower case character (t) followed directly by an upper case character (V). However, in practice, this query returns the value 1.

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