Unicode distinguishes between case mapping and case folding for this reason. The approach of lower-casing strings for comparison does not handle some Unicode special cases correctly, for example when one upper-case letter has two lower-case letter equivalents. The schema containing the citext operators must be in the current search_path (typically public) if it is not, the normal case-sensitive text operators will be invoked instead. In either situation, you will need two indexes if you want both types of searches to be fast. If you need case-insensitive behavior most of the time and case-sensitive infrequently, consider storing the data as citext and explicitly casting the column to text when you want case-sensitive comparison. The standard answer is to use the text type and manually use the lower function when you need to compare case-insensitively this works all right if case-insensitive comparison is needed only infrequently. However, citext is slightly more efficient than using lower to get case-insensitive matching.Ĭitext doesn't help much if you need data to compare case-sensitively in some contexts and case-insensitively in other contexts. Also, only text can support B-Tree deduplication. This may be changed in a future release so that both steps follow the input COLLATE specification.Ĭitext is not as efficient as text because the operator functions and the B-tree comparison functions must make copies of the data and convert it to lower case for comparisons. Currently, citext operators will honor a non-default COLLATE specification while comparing case-folded strings, but the initial folding to lower case is always done according to the database's LC_CTYPE setting (that is, as though COLLATE "default" were given). But if you have data in different languages stored in your database, users of one language may find their query results are not as expected if the collation is for another language.Īs of PostgreSQL 9.1, you can attach a COLLATE specification to citext columns or data values. Effectively, what this means is that, as long as you're happy with your collation, you should be happy with citext's comparisons. It is not truly case-insensitive in the terms defined by the Unicode standard. How it compares values is therefore determined when the database is created. Use these two functions in your sqlite queries when you want case sensitivity handled the same way as GSAK currently does now - which for many I feel is the more intuitive method.Citext's case-folding behavior depends on the LC_CTYPE setting of your database. Select * from caches where g_Contains('ü',name) Think of this as a loose replacement for the sqlite "like"įor example to get a list of caches that contain the character "ü" in the cache name and have the result be case insensitive G_contains will allow you to do a "GSAK" case insensitive search to see if the sFind string is matched anywhere in sData). GSAK two functions in sqlite to address this issue: One of the great strengths of Sqlite (and a significant reason why I chose this SQL database engine) is that it does allow you to "roll your own" functions to be used natively in any Sqlite query. Anywhere in GSAK where case is ignored (all the "contains" in a filter dialog, Upper() macro function, Replace() macro function etc) This is incongruent with native GSAK behaviour in both the existing database and macro language, as it supports the full 8bit Ansi character set when dealing with case. The result of Upper('ü') is ü instead of the expected Ü Similarly for the native sqlite Upper() function. Yet a similar query of "like '%a%'" would return anything that contained "a" or "A" However, if you used a query expression of "like '%ü%'" (like is supposed to be case insensitive) it would only return a match for the lower case ü The SQLite developers feel that adding full Unicode case tables would inflate its size unreasonably.īasically it means that you need to be aware that any character above ascii 127 will always be case sensitive when using sqlite native handling case routinesįor example, normally when ignoring case you would expect the following two characters to be the same: It is an acknowledged "bug" in SQLite which is intentionally not fixed in order to keep the library size small. When I posed the question as to why in one of the Sqlite support forums the answer went something like: Everywhere in Sqlite that refers to case, only applies to 7bit iso8859. There is one "Gotcha" in Sqlite (particularly for our European users) that I would almost call a bug.Case sensitively works differently in Sqlite than you would probably expect.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |