Column data type affected by usage of it elsewhere
Question:
I can’t seem to find a reference to the following behavior either in SQLite or apsw docs:
I have a table partially defined and populated as:
CREATE TABLE GeoLoc (lat TEXT, lon TEXT);
INSERT INTO GeoLoc (lat, lon) VALUES ('-33.5533422', '151.23422');
When using apsw to get the result for:
SELECT lat FROM GeoLoc;
I get the correct unicode value type for lat column. But running:
SELECT lat FROM GeoLoc WHERE lat + 0 = lat + 0;
I get float type instead! The above example is a silly one, but in my actual query, I’m doing some calculations with lat that turns it into floating point type but I don’t expect the type to change everywhere in my query.
I rely on exact value of lat as I stored it. When converted to float, it could change when cast back to string (see section 4.0).
Note: I get the same result with Python’s SQLite3 module, but not from as well as SQLite3’s own command line client.
Answers:
Answering my own question here. Actually when using sqlite3 CAST, it seems to work fine:
SELECT CAST(lat AS TEXT) FROM GeoLoc WHERE lat + 0 = lat + 0;
To test it, I used a very high precision floating point (e.g. 80 significant figures) and the above returned it verbatim. Appending an empty string seems to work just as well:
SELECT lat || '' FROM GeoLoc WHERE lat + 0 = lat + 0;
But, I’m still wondering why the default behavior is to change the data type all across. At least viewed from a programmer’s eyes, this is unnatural. You only expect an automatic cast to occur at the usage point.
This is a bug that was introduced in SQLite version 3.8.3.
Now fixed.
I can’t seem to find a reference to the following behavior either in SQLite or apsw docs:
I have a table partially defined and populated as:
CREATE TABLE GeoLoc (lat TEXT, lon TEXT);
INSERT INTO GeoLoc (lat, lon) VALUES ('-33.5533422', '151.23422');
When using apsw to get the result for:
SELECT lat FROM GeoLoc;
I get the correct unicode value type for lat column. But running:
SELECT lat FROM GeoLoc WHERE lat + 0 = lat + 0;
I get float type instead! The above example is a silly one, but in my actual query, I’m doing some calculations with lat that turns it into floating point type but I don’t expect the type to change everywhere in my query.
I rely on exact value of lat as I stored it. When converted to float, it could change when cast back to string (see section 4.0).
Note: I get the same result with Python’s SQLite3 module, but not from as well as SQLite3’s own command line client.
Answering my own question here. Actually when using sqlite3 CAST, it seems to work fine:
SELECT CAST(lat AS TEXT) FROM GeoLoc WHERE lat + 0 = lat + 0;
To test it, I used a very high precision floating point (e.g. 80 significant figures) and the above returned it verbatim. Appending an empty string seems to work just as well:
SELECT lat || '' FROM GeoLoc WHERE lat + 0 = lat + 0;
But, I’m still wondering why the default behavior is to change the data type all across. At least viewed from a programmer’s eyes, this is unnatural. You only expect an automatic cast to occur at the usage point.
This is a bug that was introduced in SQLite version 3.8.3.
Now fixed.