DISTINCT and ALL arguments
DISTINCT Definition
DISTINCT argument in a SELECT query specifies that only distinct rows of data can be returned.
ALL Definition
ALL argument in a SELECT query specifies that all rows of data, duplicate rows included, can be returned (default behaviour).
DISTINCT and ALL Usage
To return distinct values:
SELECT DISTINCT column1, column2,... FROM table_nameTo return all values:
SELECT ALL column1, column2,... FROM table_nameSince ALL argument is the default behaviour, the above query and
SELECT column1, column2,... FROM table_nameDISTINCT and ALL Examples
For our examples, we will use a student table.
To show all values of a first name column:
SELECT ALL FirstName FROM Student /* same as: SELECT FirstName FROM Student */
To show only unique values:
SELECT DISTINCT FirstName FROM Student