Difference between revisions of "SELECT Reference"
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Latest revision as of 13:31, 27 February 2015
The SELECT command is used to show data from a database.
The output from a SELECT statement is always a grid - with a number of rows and a number of columns.
The simplest SELECT commands involve a single table:
SELECT name, population FROM bbc WHERE region='North America'
- The SELECT line determines which columns to show - in this case
population, both of which are columns of the bbc table.
- The WHERE clause determines which rows to show
- The SELECT statement may involve data from more than one table using a JOIN or a UNION.
- SELECT statements may nested - that is the output from one SELECT may be the input to another SELECT.
- The output from a SELECT may be added to another table using INSERT .. SELECT
- The select statement may aggregate values using a SELECT .. GROUP BY clause