Postgres Compare Double Precision

1. C# Compare Double With Precision
2. Postgresql Numeric Precision

PostgreSQL offers a rich set of native data types for users. Users can add new types with the help of CREATE TYPE command. It also makes queries simpler and more readable.PostgreSQL supports the following data types:. Text Types. Numeric Types. Dates and Times.

XML. JSON. Boolean. Bits. Binary Data.

In fact, there is a limit (normally 1,000 digits), but you can adjust the limit by changing a symbol and rebuilding your PostgreSQL server from source code. The two approximate numeric types are named REAL and DOUBLE PRECISION. Table 2.4 shows the size and range for each of these data types. (9 replies) Hello, Not sure if this is the right list to ask. I vaguely remember having seen a message '. Type double precision. Will be depreciated / unsupported in future releases. ' or something like that somewhere. (?) I have quite a few older dbs with tables that have one or more fields type double precision and have so far upgraded ok since 7.0.x (I now use numeric with. Numeric vs Float Hello I have a quick question. I am thinking of applying float to replace numeric. After I would test one query I would copy the table and then drop the old table. I would then restart my postgres server to delete the cache. I did this 32 times for each data type. After designing my database with double precision.

Network. Arrays.

Create your Data Type. Boolean. Temporal. UUID. Array. JSON.

Special Data types for storing a network address and geometric data.Let's study them in detailCharacter DatatypesPostgreSQL supports character data types for storing text values. PostgreSQL builds character data types off of the same internal structures.

Not what I see: -bash-4.1$ psqlpsql (9.3.3)Type 'help' for help.postgres=# select formaterror;ERROR: x = 0.2, y = 0.2postgres=# show extrafloatdigits;extrafloatdigits-0(1 row)postgres=#That is a CentOS 6.5 server with PostgreSQL 9.3 from the yum.postgresql.org repo.So psql on the server and PgAdmin on the client agree on my machines. But Npgsql behaves differently. So something is going on in Npgsql - probably an explicit setting of extrafloatdigits on connect (?).

There is in fact an operation involved: Conversion from decimal to binary. Only a subset of decimal floating point values can be exactly represented in the binary double precision data. That's why Postgres rounds binary float values when converting to text to provide a buest guess of the original input value. Postgres=# show extrafloatdigits;extrafloatdigits-0(1 row)postgres=# select format('%s', 0.25::double precision);format-0.25(1 row)postgres=# select format('%s', 0.28::double precision);format-0.28(1 row)postgres=# select format('%s', 0.3::double precision);format-0.3(1 row)postgres=#What you get when you set extrafloatdigits higher is to get all the 'information' that Postgres can get from a binary float - including the representation errors. Postgres=# set extrafloatdigits = 3;SETpostgres=# select format('%s', 0.25::double precision);format-0.25(1 row)postgres=# select format('%s', 0.28::double precision);format-0.00000027(1 row)postgres=# select format('%s', 0.3::double precision);format-0.99999989(1 row)postgres=#I can see why you would want to bump extrafloatdigits up to avoid rounding if you transfer binary floats as text, but wire transfer of binary floats ought to be done in binary. Not to mention the localization issues you have to work around when transferring floats as text. I guess we're transfering floats in text rather than binary, right?

What do you think switching to binary for that? It would allows us to stop setting the extrafloatdigits to 3, leave it totally up to the user?Binary encoding is only used when the user prepares the command. Otherwise it is transfered as text.Not to mention the localization issues you have to work around when transferring floats as text.The localization issue is handled by using invariant culture formatting when writing the float point value:and. In the past we had complaints that those values were being sent truncated in the last digits.Isn't that more of a PostgreSQL issue than an Npgsql issue? I think it's better to leave the default value as it is, to be consistent with other client libraries. If the users really want different float representations, they can manually set extrafloatdigits.I think I agree with here - forcing non-default Postgresql behavior on Npgsql users (i.e.

C# Compare Double With Precision

Increased precision) seems problematic, and the strange default behavior described in this issue is a good example (where instead of 0.3 users get 0.99999989 by default).However, I admit I don't know what kind of trouble users had in the first place when the extrafloatdigits wasn't set., do you remember what kind of trouble caused this in the first place? How would you feel about removing the extrafloatdigits setting in Npgsql for 3.0? Hi all!The root of the extrafloatdigits handling is this bug report about double precision numbers handling:Then, I imported Udo Liess test case to our test suite and created the Bug1010992DoubleValueSupport test:I agree with as well and I'd add a connection string parameter which would let the user specify how many digits she wants to use?I'm saying that because although the user can set the value with a query, I think it wouldn't be very practical to set it every time a connection was created. I think a connection string parameter would simplify a lot this process.

Postgresql Numeric Precision

The Bug1010992DoubleValueSupport test seems to make an assert that is too strict, if I understand floating point properly. In general, when comparing floats one always sets a 'tolerance' (or 'epsilon') value, within which differences are tolerated - see the section on float comparison. Among other things, this is because floating point arithmetic does not always yield the expected result (e.g. (x. 0.5) / 0.5 isn't necessarily exactly equal to x).In other words, I think it's perfectly acceptable for Bug1010992DoubleValueSupport to fail as it's currently written.I guess we're in agreement to stop setting extrafloatdigits in Npgsql 3.0, and leave it up to the user, right?, it's possible to add this as a connection string parameter but I'm not sure about the usefulness - why provide it for this parameter and not for any/all other parameters Postgresql supports? Also, connection string parameters are important for connection pooling - connections with different extrafloatdigits won't be reused by the pool, although they are in essence the same.I'm not really that against an extrafloatdigits connstring param, I'm just not sure it make that much sense. Let me know what you think.