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SQL-92 was the third revision of the SQL database query language. Unlike SQL-89, it was a major revision of the standard. Aside from a few minor incompatibilities, the SQL-89 standard is forward-compatible with SQL-92. The standard specification itself grew about five times compared to SQL-89.
The time 2 48 × 4 μs after 1980 started was 2015-09-05 05:58:26.84262 UTC. Thus, the last time at which UUIDs could be generated in this original format was in 2015. [20] time_low 0x04: 2 octets / 16 bits reserved 0x06: 2 octets / 16 bits These octets are reserved for future use. family 0x08: 1 octet / 8 bits This octet is an address family ...
The format was created by Twitter (now X) and is used for the IDs of tweets. [1] It is popularly believed that every snowflake has a unique structure, so they took the name "snowflake ID". The format has been adopted by other companies, including Discord and Instagram. The Mastodon social network uses a modified version.
In SQL, the unique keys have a UNIQUE constraint assigned to them in order to prevent duplicates (a duplicate entry is not valid in a unique column). Alternate keys may be used like the primary key when doing a single-table select or when filtering in a where clause, but are not typically used to join multiple tables.
A surrogate key is frequently a sequential number (e.g. a Sybase or SQL Server "identity column", a PostgreSQL or Informix serial, an Oracle or SQL Server SEQUENCE or a column defined with AUTO_INCREMENT in MySQL). Some databases provide UUID/GUID as a possible data type for surrogate keys (e.g. PostgreSQL UUID [3] or SQL Server ...
A unique identifier (UID) is an identifier that is guaranteed to be unique among all identifiers used for those objects and for a specific purpose. [1] The concept was formalized early in the development of computer science and information systems.
Varchar fields can be of any size up to a limit, which varies by databases: an Oracle 11g database has a limit of 4000 bytes, [1] a MySQL 5.7 database has a limit of 65,535 bytes (for the entire row) [2] and Microsoft SQL Server 2008 has a limit of 8000 bytes (unless varchar(max) is used, which has a maximum storage capacity of 2 gigabytes).
One of the reasons to have date dimensions is to place calendar knowledge in the data warehouse instead of hard-coded in an application. While a simple SQL date-timestamp is useful for providing accurate information about the time a fact was recorded, it can not give information about holidays, fiscal periods, etc. An SQL date-timestamp can ...