SQL (Single table queries)

What is the basic form of the SQL SELECT command

SELECT-FROM-WHERE. Specify the columns to be listed after the word SELECT (or asterisk (*) to select all columns). Then specify the table name after the work FROM. Optionally, you can include one or more conditions after the word WHERE.

How are simple conditions written?

Column name, comparison operator, column name or value.

What comparison operators can be used with simple conditions?

=,>,>=,<,<=,<>, or !=

How are compound conditions formed?

By combining simple conditions using the AND, OR, and NOT operators

BETWEEN operator

Indicates a range of values in a condition. Also used to determine whether a value is between two other values without using an AND condition.

How do you use computed columns in SQL commands?

By using arithmetic operators an writing the computation in place of a column name

How do you assign a name to a computed column?

Follow the computation with the word AS and then the name

LIKE operator

Used to check for a value in a character column that is similar to a particular string of characters

Use of (%), ( _ ) wildcards

The percent (%) wildcard represents any collection of characters. The underscore ( _ ) wildcard represents any single character.

IN operator

Used to determine whether a column contains a value in a set of values

Aggregate functions COUNT, SUM, AVG, MAX, and MIN

SQL processes these aggregate functions to calculate values for groups of rows

What command do you use to sort data?

Use an ORDER BY clause

What is a Major Sort Key (or the Primary Sort Key)

The more important column when sorting data on two columns

What is a Minor Sort Key (or the Secondary Sort Key)

The less important column when sorting data on two columns

How do you sort data in descending order?

Follow the sort key with the DESC operator

How do you avoid including duplicate values in a query's result?

To avoid duplicates, precede the column name with the DISTINCT operator

What is a subquery?

When one SQL query is placed inside another, it is called a subquery.

How do you find rows in which a particular column contains a null value?

Use the IS NULL operator in the WHERE clause

How do you group data in a SQL query?

Use a GROUP BY clause

When grouping data in a query, how do you restrict the output to only those groups satisfying some condition?

Use a HAVING clause to restrict the output to certain groups.