I have a mysql database with a table X having float unsigned column amount.
The value is saved properly with two decimal places when the value is less than 10000.
But for data more than that it is rounding off two decimal places to one.
I am not sure if >10000 is causing this but thats the primary suspect.
The value is being mapped to Float amount in the application entity.
I don't know why numbers are getting rounded off for some amount values.
Did anyone face similar issue?
MySQL performs rounding when storing values according to the length of Float column. The quick fix is to set the length of the Float column in your MySql table e.g. FLOAT(11,2)
MySQL reference can be found here: Floating-Point Types (Approximate Value).
Related
I have many float columns, But in phpmyadmin I didn't provide the size of float but unlike varchar, it still saves the column
what is the default size of float?
should I enter the size manually like Float(10,2) Or it does not make much performance difference ?
Thanks :)
As mysql manual on float says:
For maximum portability, code requiring storage of approximate numeric data values should use FLOAT or DOUBLE PRECISION with no specification of precision or number of digits.
No length is the default length value.
However, if you do specify length, then mysql will round the float to the number of decimals specified. See the documentation linked above for more details:
For example, a column defined as FLOAT(7,4) will look like -999.9999 when displayed. MySQL performs rounding when storing values, so if you insert 999.00009 into a FLOAT(7,4) column, the approximate result is 999.0001.
I am entering '35444650.00' as a float into my MySQL and it keeps reformatting to 35444648.00, any help welcome...
Floats only have a certain level of precision, you may be going beyond how precise a float data type can be. Try using a DOUBLE instead.
A float has 6 digits of precision. Use a double to get 15 or switch to a numeric(x,y). If you're interested, check out the storage requirements for MySQL for the different data types.
The MySQL manual claims that FLOAT, REAL, and DOUBLE PRECISION fields stores values as approximate and INTEGER, SMALLINT, DECIMAL, and NUMERIC fields stores values as exact.
I think best bet to overcome this precision issue is to use decimal.
Reference: http://dev.mysql.com/doc/refman/5.1/en/numeric-types.html
A higher precision alternative to float is DOUBLE. But looking at the example, I think the DECIMAL datatype might come in handy if the number of digits required after zero is small (around 2-4) and the number of digits before decimal is also small (around 10-12).
You are going past the level of precision possible. You need to define the float with more precision, i.e. "FLOAT(10,5)" would mean a float that can have 10 digits total with up to five after the decimal point.
I have a table with high precision value, stored as Float. When I query the table for that value it returns rounded off value, rounded to 1st digit. But when I run the below query I am getting the value that I have stored,
SELECT MY_FLOAT_COL*1 FROM MY_TABLE;
What's going on inside Mysql?
If you want to store exact values, you'd use the DECIMAL data types.
By manual of FLOAT:
The FLOAT and DOUBLE types represent approximate numeric data values. MySQL uses four bytes for single-precision values
The thing to mention here is approximation.
You can read more on floats here: http://dev.mysql.com/doc/internals/en/floating-point-types.html
I'm somewhat confused on defining the correct definition for a float table column. This is required to create a database table to store large numbers which have up to eight decimal places. I need to be able to store anywhere from and between the following two.
0.00000001 - 10000000
Would that be defined as float(16) as the argument is the maximum number of digits that need to be displayed. Perhaps I have misunderstood the column definition entirely.
FLOAT is approximate datatype and I would not recommend it to use for storing exact values.
For storing exact numbers you should use DECIMAL datatype:
CREATE TABLE tab(col DECIMAL(20,10));
Should be more than sufficent for your needs.
I use the Navicat MySQL GUI and have noticed there are Length and Decimal settings for all columns:
I understand the how the length and decimals settings work for float and decimal data types, but do they matter for other column types such as int and datetime?
MySQL doesn't use the term "Decimals", so that must be a term decided upon in the GUI tool you're using when defining DECIMAL or FLOAT types. For authoritative information, consult the GUI tool's documentation on how these settings affect types they wouldn't normally seem to apply to.
Searching around Navicat's documentation turns up little of any use on how it expects "Length" and "Decimals" to apply to integer and date types:
se the Length edit box to define the length of the field and use Decimals edit box to define the number of digits after the decimal point (the scale) for Floating Point data type.
...so not really helpful.
MySQL has a few options for storage length of integer types (which limit the maximum size of the integer that the column can hold), but those limits are specified by the name of the data type rather than a numeric length specified in the column definition.
This table of INT types explains the numeric ranges possible for each named type.
MySQL also offers an option on the integer types in the form of a display length like INT(11) which affects the displayed value rather than the stored value when using the ZEROFILL option.. Your GUI editor appears to map its "Length" option to the integer zerofill attribute.
See also: What is the benefit of ZEROFILL in MySQL?
How to find out, absent good documentation:
However, when working with a GUI client and not understanding what it is doing under the hood, the best advice I can offer would be to try out different settings and then examine the output of SHOW CREATE TABLE <tablename> to see what DDL statement the GUI ultimately constructed and sent to the RDMBS.
Syntax reference: SHOW CREATE TABLE
For datetime, it specifies the precision, and is a number up to 6. 3 will give you milliseconds and 6 will give you microseconds (millionth of a second). The length of an INT changes how the value is displayed, but it will still store the same value.