Sorting data and Other selection Techniques

Ordering data results

Allows us to view our data in a more meaningful way. Rather than just a list of raw data, we can sort on one or many different criteria. This will allow us and/or the user to focus on the items of interest.

ORDER BY clause

Simplest form:

SELECT column

FROM table

ORDER BY column

Nested OrderingOrdering can occur on a number of levels. When you

ORDER BY on more than one column the first column takes highest precedence and goes down the line.

Example:SELECT author, price, title

FROM booksORDER BY price, title, author

The results would be ordered by price, then title and then author… in ascending order. Ascending order is the default.

Sort order

We can change sort order using the

DESC (for descending) and ASC (for

ascending) keywords.Example:

SELECT author, title, price

FROM books

ORDER BY price desc, author

Note: author would still be sorted ascending. DESC only affects the price column.

Ordering ExpressionsWhen we want to order expressions we

need to refer to the expression by its alias or its position.

Example:SELECT price * .9 disc, author, title

FROM booksORDER BY disc, title

orODER BY 1, title

Eliminating DuplicatesALL the default returns all qualified rows

DISTINCT returns only unique when more than 1 item in SELECT list, returns only the unique

combinations.

Both can only occur once and only at the beginning of the SELCT list.

SELECT DISTINCT book_storeFROM stores

Non-select list Order ByOn systems that allow it, having a

column listed in the ORDER BY and not in the SELECT list broadens the scope of the query to include that column as well.

The column is NOT displayed in the results. Only the affected rows.

Grouping data

Grouping data allows us to view aggregated data in reference to a field of interest. This makes for a powerful reporting tool.

GROUP BY clause

Groups results by column name

used with aggregate functions

SyntaxSELECT col_1, max(col_2) FROM table

GROUP BY col_1column in GROUP BY must be in SELECT listThere can be multiple columns in GROUP BY. Where their list order is their order of precedence.

Limitations

•There must be only 1 value returned for

each GROUP BY field.

•Should only use column names

•Due to these limitations, many vendors

provide report generators

Grouping and NullsNulls are assigned a group of there own

since they are, in a sense, their own datatype.

HAVING clauseSame as WHERE clause except it

allows aggregate functions

Formatting TextgetDate() - returns today’s dateSELECT getDate()

char_length(data) - returns the lengthSELECT char_length(‘John’)

upper(data) - returns the uppercaselower(data) - returns the lowercaseconcatonation SELECT (name +` `+address+`,`+state)