SQL Guide: Getting Started

Query — a request for data or information from a database

Basic Structure of a SQL query

SELECT

    [choose the column(s) you want] #2

FROM

    [from the appropriate table] #1

WHERE

    [a certain condition is met] #3

Numbers next to description is suggested order in which you would write your SQL queries.

SELECT — choose the columns you want to return

FROM — choose the tables where the columns you want are located

WHERE — filter for certain information

Example of a Query

SELECT first_name 
FROM customer_data.customer_name
WHERE first_name = 'Tony'

The above query uses three commands to locate the customers with the first name, Tony.

1. SELECT the column name first_name

2. FROM a table named customer_name (in a dataset named customer_data) (The dataset name is always followed by a dot, and then the table name.)

3. But only return the data WHERE the first_name is 'Tony'

Result:

Multiple Columns in a Query

If requesting multiple data fields from a table:

SELECT
    ColumnA,
    ColumnB,
    ColumnC
FROM
    Table where the data lives
WHERE
    Certain condition is met

Example of how it would appear:

SELECT
    customer_id,
    first_name,
    last_name
FROM
    customer_data.customer_name
WHERE
    first_name = 'Tony'

The above query uses three commands to locate customers with the first_name, 'Tony'.

1. SELECT the columns named customer_id, first_name, and last_name

2. FROM a table named customer_name (in a dataset named customer_data) (The dataset name is always followed by a dot, and then the table name.)

3. But only return the data WHERE the first_name is 'Tony'

Another example:

SELECT
ColumnA,
ColumnB,
ColumnC
FROM
	Table where the data lives
WHERE
	Condition 1
	AND Condition 2
	AND Condition 3

Example of how it would appear:

SELECT
	customer_id,
	first_name,
	last_name
FROM
	customer_data.customer_name
WHERE
	customer_id > 0
	AND first_name = 'Tony'
	AND last_name = 'Magnolia'

The above query uses three commands to locate customers with a valid (greater than 0), customer_id whose first_name is 'Tony' and last_name is 'Magnolia'.

1. SELECT the columns named customer_id, first_name, and last_name

2. FROM a table named customer_name (in a dataset named customer_data) (The dataset name is always followed by a dot, and then the table name.)

3. But only return the data WHERE customer_id is greater than 0, first_name is Tony, and last_name is Magnolia.

Results:

If only one customer is named Tony Magnolia, the results from the query could be:

If more than one customer has the same name, the results from the query could be: