DBMS & SQL Previous Year Questions (page 5)

Explanation

The HR tag supports SIZE, WIDTH, ALIGN and NOSHADE. There is no SHADE attribute.

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set_index() takes a column name or list of column names and returns a new DataFrame indexed by those columns.

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pandas merge() joins DataFrames on common columns, like SQL joins, so tables can be combined as in a database.

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CEILING returns the smallest integer greater than or equal to the value, e.g. CEILING(4.2) = 5. FLOOR returns the largest integer less than or equal to it.

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SELECT * retrieves all attributes (columns) of the selected tuples.

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The semantic analyzer checks meaning and gathers type information, storing it in the syntax tree or symbol table for intermediate code generation.

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SQL aggregate functions include COUNT, SUM, AVG, MAX and MIN. Cross product is a relational join operation, not an aggregate.

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Per Elmasri-Navathe, an entity type defines a collection of entities that have the same attributes; the actual set of entities at a moment is the entity set.

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In ER-to-relational mapping, a 1:1 or 1:N relationship type corresponds to a foreign key (or a relationship relation) in the relational model.

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Referential integrity is specified between two relations: a foreign key value must match an existing primary key in the referenced relation, keeping tuples consistent.

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|| is the standard SQL string concatenation operator, e.g. 'ab' || 'cd' gives 'abcd'.

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LIKE is used in WHERE for pattern matching with wildcards % and _, e.g. WHERE name LIKE 'A%'.

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DROP SCHEMA name RESTRICT removes the schema only if it has no elements; CASCADE would drop it with all its contents.

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Profit is the excess of revenue over expenses. It can be worked out for a single transaction or for the whole business over a period.

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A primary key uniquely identifies each row in its table. A foreign key refers to a primary key in another table, which links the tables.

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A join combines rows from several tables on a related (common) column. A subquery is a query nested inside another query, often used to filter on a condition.

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B-tree indexes keep keys in sorted, hierarchical order, so they handle range queries well. Hash indexes use a hash function, which is good for exact-match lookups but not ranges.

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A foreign key is a column in one table that refers to the primary key of another table.

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Per the key, a database, MIS executives and control and maintenance of the MIS are the core prerequisites of a good MIS, while staff support is not counted as one.

Explanation

The shift operator satisfies Ef(x) = f(x + h), and Δf(x) = f(x + h) − f(x) = (E − 1)f(x). So Δ = E − 1, which means E = 1 + Δ.

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A zombie process has finished executing, but its entry stays in the process table until the parent reads its exit status with wait().

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DDL commands (CREATE, ALTER, DROP) define and change the structure (schema) of relations and remove them. DML only queries and modifies the data stored in them.

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An XML processor (parser) reads XML documents and gives applications access to their content and structure, for example through DOM or SAX. An XML schema only defines the valid structure.

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In a relational database, data is stored in tables (relations) of rows and columns, and the tables are linked through keys. Fields and records are just parts of a table.

Explanation

Armstrong's axioms are only reflexivity, augmentation and transitivity. Pseudo-transitivity is a derived rule (inferred from these axioms), not one of the axioms themselves.

Explanation

fork() splits a process into concurrent parts, and join() waits for them to finish and recombine. Together they form a complete concurrent subroutine; sleep() only suspends execution.

Explanation

Web browsers act as a universal client (front end) for web-based database applications. They send requests over the Internet to the web or application server that connects to the back-end database.