Overview
A relational database management system 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
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