SELECTsetninger

SELECTsetninger are fundamental statements in SQL (Structured Query Language) used to retrieve data from one or more tables in a relational database. The core of a SELECT statement is the SELECT keyword, followed by a list of columns to be retrieved. This list can include specific column names, or an asterisk (*) to indicate all columns.

Following the SELECT clause is the FROM clause, which specifies the table(s) from which the data should be fetched. When data is needed from multiple tables, they are listed in the FROM clause, often with JOIN conditions to link related rows.

The WHERE clause is optional and is used to filter the rows returned by the query. It specifies conditions that must be met for a row to be included in the result set. Conditions can involve comparisons, logical operators (AND, OR, NOT), and various built-in functions.

Other optional clauses further refine the data retrieval process. The GROUP BY clause is used to aggregate rows that have the same values in specified columns, often in conjunction with aggregate functions like COUNT, SUM, AVG, MIN, or MAX. The HAVING clause is used to filter groups created by the GROUP BY clause, similar to how WHERE filters individual rows. Finally, the ORDER BY clause sorts the result set in ascending (ASC) or descending (DESC) order based on one or more specified columns.