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In addition to basic equality and inequality conditions, SQL allows for more complex conditional logic through constructs such as CASE, COALESCE, and NULLIF.The CASE expression, for example, enables SQL to perform conditional branching within queries, providing a mechanism to return different values based on evaluated conditions.
Predicates, which specify conditions that can be evaluated to SQL three-valued logic (3VL) (true/false/unknown) or Boolean truth values and are used to limit the effects of statements and queries, or to change program flow. Queries, which retrieve the data based on specific criteria. This is an important element of SQL.
A relational database management system uses SQL MERGE (also called upsert) statements to INSERT new records or UPDATE or DELETE existing records depending on whether condition matches. It was officially introduced in the SQL:2003 standard, and expanded [citation needed] in the SQL:2008 standard.
Most database management systems restrict check constraints to a single row, with access to constants and deterministic functions, but not to data in other tables, or to data invisible to the current transaction because of transaction isolation. Such constraints are not truly table check constraints but rather row check constraints.
A table (called the referencing table) can refer to a column (or a group of columns) in another table (the referenced table) by using a foreign key.The referenced column(s) in the referenced table must be under a unique constraint, such as a primary key.
SQL was initially developed at IBM by Donald D. Chamberlin and Raymond F. Boyce after learning about the relational model from Edgar F. Codd [12] in the early 1970s. [13] This version, initially called SEQUEL (Structured English Query Language), was designed to manipulate and retrieve data stored in IBM's original quasirelational database management system, System R, which a group at IBM San ...
This would allow any customer to be serviced without waiting for another customer who is accessing a different account. This is analogous to a record level lock and is normally the highest degree of locking granularity in a database management system. In a SQL database, a record is typically called a "row".
The techniques used in white box testing are condition coverage, decision coverage, statement coverage, cyclomatic complexity. The main advantage of white box testing in database testing is that coding errors are detected, so internal bugs in the database can be eliminated. The limitation of white box testing is that SQL statements are not covered.