BigDecimal variable padded with random numbers in JDBC Insert

问题

Consider SQL statement INSERT INTO table (field) VALUES (-0.11111111) with field Oracle type NUMBER.

When the value to be inserted is of type float or double, you get the exact value in field, i.e. -0.11111111.

But when the value to be inserted is of type BigDecimal, you get the value padded with random numbers, i.e. 0.1111111099999999990428634077943570446223.

Why?

Java states that "BigDecimal is an immutable, arbitrary-precision signed decimal numbers."

The code is:

String sql = "INSERT INTO pat_statistics (file_key,test_number,rqw)"
    + " VALUES (3778, 100, " + new BigDecimal(-0.11111111) + ")";
Class.forName(driver);
Connection conn = DriverManager.getConnection(url, user, pwd);
Statement st = conn.createStatement();
int n = st.executeUpdate(sql);

The DB is Oracle.

回答1:

For a literal value you should always use the BigDecimal constructor taking a string argument. See the documentation of the BigDecimal(double) constructor for details.

回答2:

You are creating the BigDecimal from a float so it will reflect exactly the value of the float, and as you probably know the trailing digits of a float are more ore less random.

I assume you see this int he database because the jdbc driver thinks: Hey I am getting a BigDecimal. I can use all the digits I can master.

When you use float or double the jdbc driver knows I cann't rely on all the digits and ignores what comes after that threshhold.

If you need the additional precision of Big Decimal, create it from a String or calculate it from Integegers.

=== another correction ====

The handling is not done by the jdbc driver, but by the various toString conversions, since you are assembling your SQL String.

BTW: you really should use bind variables for this.

来源：https://stackoverflow.com/questions/5074735/bigdecimal-variable-padded-with-random-numbers-in-jdbc-insert

标签

java

Oracle

precision

bigdecimal