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MEMORY is a storage engine for MySQL and MariaDB relational database management systems, developed by Oracle and MariaDB. Before the version 4.1 of MySQL it was called Heap. The SHOW ENGINES command describes MEMORY as: Hash based, stored in memory, useful for temporary tables. MEMORY writes table data in-memory.
A new information schema—read-only views about database metadata like what tables it contains, etc. For example, SELECT * FROM INFORMATION_SCHEMA.TABLES;. Dynamic execution of queries (as opposed to prepared). Better support for remote database access. Temporary tables; CREATE TEMP TABLE etc. Transaction isolation levels.
A common table expression, or CTE, (in SQL) is a temporary named result set, derived from a simple query and defined within the execution scope of a SELECT, INSERT, UPDATE, or DELETE statement. CTEs can be thought of as alternatives to derived tables ( subquery ), views , and inline user-defined functions.
A true fully (database, schema, and table) qualified query is exemplified as such: SELECT * FROM database. schema. table. Both a schema and a database can be used to isolate one table, "foo", from another like-named table "foo". The following is pseudo code: SELECT * FROM database1. foo vs. SELECT * FROM database2. foo (no explicit schema ...
Views can represent a subset of the data contained in a table. Consequently, a view can limit the degree of exposure of the underlying tables to the outer world: a given user may have permission to query the view, while denied access to the rest of the base table. [2] Views can join and simplify multiple tables into a single virtual table. [2]
LDB – Temporary database file, only existing when database is open; LIRS – Layered Intager Storage. Stores intageres with characters such as semicolons to create lists of data. MDA – Add-in file for Microsoft Access; MDB – Microsoft Access database; ADP – Microsoft Access project (used for accessing databases on a server)
Each MyISAM table is stored on disk in three files (if it is not partitioned). The files have names that begin with the table name and have an extension to indicate the file type. MySQL uses a .frm file to store the definition of the table, but this file is not a part of the MyISAM engine; instead it is a part of the server.
A derived table is the use of referencing an SQL subquery in a FROM clause. Essentially, the derived table is a subquery that can be selected from or joined to. The derived table functionality allows the user to reference the subquery as a table. The derived table is sometimes referred to as an inline view or a subselect.