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4.5.5 Java, JDBC, and MySQL Types

MySQL Connector/J is flexible in the way it handles conversions between MySQL data types and Java data types.

In general, any MySQL data type can be converted to a java.lang.String, and any numeric type can be converted to any of the Java numeric types, although round-off, overflow, or loss of precision may occur.


All TEXT types return Types.LONGVARCHAR with different getPrecision() values (65535, 255, 16777215, and 2147483647 respectively) with getColumnType() returning -1. This behavior is intentional even though TINYTEXT does not fall, regarding to its size, within the LONGVARCHAR category. This is to avoid different handling inside the same base type. And getColumnType() returns -1 because the internal server handling is of type TEXT, which is similar to BLOB.

Also note that getColumnTypeName() will return VARCHAR even though getColumnType() returns Types.LONGVARCHAR, because VARCHAR is the designated column database-specific name for this type.

Connector/J issues warnings or throws DataTruncation exceptions as is required by the JDBC specification, unless the connection was configured not to do so by using the property jdbcCompliantTruncation and setting it to false.

The conversions that are always guaranteed to work are listed in the following table. The first column lists one or more MySQL data types, and the second column lists one or more Java types to which the MySQL types can be converted.

Table 4.5 Possible Conversions Between MySQL and Java Data Types

These MySQL Data TypesCan always be converted to these Java types
CHAR, VARCHAR, BLOB, TEXT, ENUM, and SETjava.lang.String,,, java.sql.Blob, java.sql.Clob
FLOAT, REAL, DOUBLE PRECISION, NUMERIC, DECIMAL, TINYINT, SMALLINT, MEDIUMINT, INTEGER, BIGINTjava.lang.String, java.lang.Short, java.lang.Integer, java.lang.Long, java.lang.Double, java.math.BigDecimal
DATE, TIME, DATETIME, TIMESTAMPjava.lang.String, java.sql.Date, java.sql.Timestamp


Round-off, overflow or loss of precision may occur if you choose a Java numeric data type that has less precision or capacity than the MySQL data type you are converting to/from.

The ResultSet.getObject() method uses the type conversions between MySQL and Java types, following the JDBC specification where appropriate. The values returned by ResultSetMetaData.GetColumnTypeName()and ResultSetMetaData.GetColumnClassName() are shown in the table below. For more information on the JDBC types, see the reference on the java.sql.Types class.

Table 4.6 MySQL Types and Return Values for ResultSetMetaData.GetColumnTypeName()and ResultSetMetaData.GetColumnClassName()

MySQL Type NameReturn value of GetColumnTypeNameReturn value of GetColumnClassName
BIT( > 1)BITbyte[]
TINYINTTINYINTjava.lang.Boolean if the configuration property tinyInt1isBit is set to true (the default) and the storage size is 1, or java.lang.Integer if not.
BOOL, BOOLEANTINYINTSee TINYINT, above as these are aliases for TINYINT(1), currently.
SMALLINT[(M)] [UNSIGNED]SMALLINT [UNSIGNED]java.lang.Integer (regardless of whether it is UNSIGNED or not)
MEDIUMINT[(M)] [UNSIGNED]MEDIUMINT [UNSIGNED]java.lang.Integer (regardless of whether it is UNSIGNED or not)
INT,INTEGER[(M)] [UNSIGNED]INTEGER [UNSIGNED]java.lang.Integer, if UNSIGNED java.lang.Long
BIGINT[(M)] [UNSIGNED]BIGINT [UNSIGNED]java.lang.Long, if UNSIGNED java.math.BigInteger
YEAR[(2|4)]YEARIf yearIsDateType configuration property is set to false, then the returned object type is java.sql.Short. If set to true (the default), then the returned object is of type java.sql.Date with the date set to January 1st, at midnight.
CHAR(M)CHARjava.lang.String (unless the character set for the column is BINARY, then byte[] is returned.
VARCHAR(M) [BINARY]VARCHARjava.lang.String (unless the character set for the column is BINARY, then byte[] is returned.