A
relational database management system
A relational database is a (most commonly digital) database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relatio ...
uses
SQL conditions or
expressions in
clauses and in
clauses to subsets of data.
Types of condition
* Many conditions compare values for (for example) equality, inequality or similarity.
* The EXISTS condition uses the
SQL standard keyword
EXISTS to determine whether rows exist in a
subquery result.
[
]
Examples
To one row of data from a table called ''tab'' with a primary key column (''pk'') set to 100 — use the condition ''pk = 100'':
SELECT * FROM tab WHERE pk = 100
To identify whether a table ''tab'' has rows of data with a duplicated column ''dk'' — use the condition ''having count(*) > 1'':
SELECT dk FROM tab GROUP BY dk HAVING count(*) > 1
References
{{DEFAULTSORT:Condition (Sql)
SQL
Articles with example SQL code