Data types

Data types. These data type changes have been implemented:
• MySQL now permits fractional seconds for TIME, DATETIME, and TIMESTAMP values, with up to
microseconds (6 digits) precision. See Section 11.3.6, “Fractional Seconds in Time Values”.
• Previously, at most one TIMESTAMP column per table could be automatically initialized or
updated to the current date and time. This restriction has been lifted. Any TIMESTAMP column
definition can have any combination of DEFAULT CURRENT_TIMESTAMP and ON UPDATE
CURRENT_TIMESTAMP clauses. In addition, these clauses now can be used with DATETIME
column definitions. For more information, see Section 11.3.5, “Automatic Initialization and
Updating for TIMESTAMP and DATETIME”.
• In MySQL, the TIMESTAMP data type differs in nonstandard ways from other data types in
terms of default value and assignment of automatic initialization and update attributes. These
behaviors remain the default but now are deprecated, and can be turned off by enabling the
explicit_defaults_for_timestamp [495] system variable at server startup. See
Section 11.3.5, “Automatic Initialization and Updating for TIMESTAMP and DATETIME”, and
Section 5.1.4, “Server System Variables”.
• The YEAR(2) data type is now deprecated. YEAR(2) columns in existing tables are treated as
before, but YEAR(2) in new or altered tables are converted to YEAR(4). For more information,
see Section 11.3.4, “YEAR(2) Limitations and Migrating to YEAR(4)”.
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