Postgres Transpose Rows to Columns Based on Column Value

Question

I have the following statement table in Postgres:

stock |  year | statement    | amount           

ACME  | 2003  | Q1 Earnings  | 100
ACME  | 2003  | Q2 Earnings  | 200
ACME  | 2004  | Q2 Earnings  | 300

How do I make a new table with all of a year's 4 quarters on one row? And null values for missing statements.

stock | year | Q1 Earnings | Q2 Earnings | Q3 Earnings | Q4 Earnings 

ACME  | 2003 | 100         | 200         | Null        | Null
ACME  | 2004 | NULL        | 300         | Null        | Null

Found this answer: Postgres - Transpose Rows to Columns but it doesn't show how to create and populate the new columns based on another value or deal with null values.

Tim Biegeleisen · Accepted Answer · 2021-06-02 03:20:19Z

9

Assuming you have a fixed 4 quarters per year which you want to display, use pivoting logic:

SELECT
    stock,
    year,
    MAX(amount) FILTER (WHERE statement = 'Q1 Earnings') AS "Q1 Earnings",
    MAX(amount) FILTER (WHERE statement = 'Q2 Earnings') AS "Q2 Earnings",
    MAX(amount) FILTER (WHERE statement = 'Q3 Earnings') AS "Q3 Earnings",
    MAX(amount) FILTER (WHERE statement = 'Q4 Earnings') AS "Q4 Earnings"
FROM statement
GROUP BY
    stock,
    year;

answered Jun 2, 2021 at 3:20

Tim Biegeleisen

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2 Comments

user2415706 Over a year ago

Thank you. Does this automatically take care of NULL values?

Tim Biegeleisen Over a year ago

If a given stock and year have no data for a certain quarter, then the above would just report NULL in that case. You may use COALESCE to display some backup value if you want.

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