This command will yield the names of authors from the relation book_author whose age is greater than 50. WHERE − This clause defines predicate or conditions, which must match in order to qualify the attributes to be projected. In case more than one relation names are given, this clause corresponds to Cartesian product. It selects the attributes based on the condition described by WHERE clause.įROM − This clause takes a relation name as an argument from which attributes are to be selected/projected. It is similar to the projection operation of relational algebra. SELECT − This is one of the fundamental query command of SQL. These basic constructs allow database programmers and users to enter data and information into the database and retrieve efficiently using a number of filter options. SQL contains the following set of commands in its DML section − DML is responsible for all forms data modification in a database. DML modifies the database instance by inserting, updating and deleting its data. SQL is equipped with data manipulation language (DML). This command adds an attribute in the relation article with the name subject of string type.
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SQL uses the following set of commands to define database schema − CREATEĬreates new databases, tables and views from RDBMS.ĭrops commands, views, tables, and databases from RDBMS.Īlter object_type object_name parameters Using the data definition properties of SQL, one can design and modify database schema, whereas data manipulation properties allows SQL to store and retrieve data from database. SQL comprises both data definition and data manipulation languages. SQL comes as a package with all major distributions of RDBMS. It is designed over relational algebra and tuple relational calculus.
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SQL is a programming language for Relational Databases.