Declarative over Procedural
The DB System philosophy: “Tell the DBS what you want”.
Data Manipulation Languages (DMLs) are for querying/updating data and should be declarative; say what you want, but not how to do it.
Why? Query Optimisation: the DBS will find an optimal (or close to) way to execute query.
Data Definition Languages (DDLs) are for defining the DB.
Content to be organised later
SELECT CU.first_name AS fn, CU.age AS ag, CU.age*2 AS doubledAge
FROM Customers AS CU WHERE ag > 25;
-- American query
SELECT C.first_name 'First Name', 'American''s!' Nationality FROM Customers C WHERE C.country='USA';REMEMBER Create Table is a statement, requiring a ;
Scalar Subquery error:
ERROR: more than one row returned by a subquery used as an expression