Databases Interview Questions

What does it mean to have QUOTED_IDENTIFIER ON? What are the Implications of having it OFF?

General

Written by abnotaLok Monday, 09 January 2012 17:37

When SET QUOTED_IDENTIFIER is ON, identifiers can be delimited by double quotation marks, and literals must be delimited by single quotation marks. When SET QUOTED_IDENTIFIER is OFF, identifiers cannot be quoted and must follow all T-SQL rules for identifiers.

 

What is the Difference between a Local and a Global Temporary Table?

General

Written by abnotaLok Monday, 09 January 2012 17:37

A local temporary table exists only for the duration of a connection, or if defined inside a compound statement, for the duration of the compound statement.

A global temporary table remains in the database accessible across the connections. Once the connection where original global table is declared dropped this becomes unavailable.

What is the STUFF Function and How Does it Differ from the REPLACE Function?

General

Written by abnotaLok Monday, 09 January 2012 17:37

STUFF function is used to overwrite existing characters using this syntax: STUFF (string_expression, start, length, replacement_characters), where string_expression is the string that will have characters substituted, start is the starting position, length is the number of characters in the string that are substituted, and replacement_characters are the new characters interjected into the string. REPLACE function is used to replace existing characters of all occurrences. Using the syntax REPLACE (string_expression, search_string, replacement_string), every incidence of search_string found in the string_expression will be replaced with replacement_string.

 

What is PRIMARY KEY?

General

Written by abnotaLok Monday, 09 January 2012 17:37

A PRIMARY KEY constraint is a unique identifier for a row within a database table. Every table should have a primary key constraint to uniquely identify each row, and only one primary key constraint can be created for each table. The primary key constraints are used to enforce entity integrity.

What is UNIQUE KEY Constraint?

General

Written by abnotaLok Monday, 09 January 2012 17:37

A UNIQUE constraint enforces the uniqueness of the values in a set of columns; so no duplicate values are entered. The unique key constraints are used to enforce entity integrity as the primary key constraints.

 

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