Does any one know how to create crosstab queries in PostgreSQL?
For example I have the following table:
Section Status Count A Active 1 A Inactive 2 B Active 4 B Inactive 5 I would like the query to return the following crosstab:
Section Active Inactive A 1 2 B 4 5 Is this possible?
16 Answers
Install the additional module tablefunc once per database, which provides the function crosstab(). Since Postgres 9.1 you can use CREATE EXTENSION for that:
CREATE EXTENSION IF NOT EXISTS tablefunc; Improved test case
CREATE TABLE tbl ( section text , status text , ct integer -- "count" is a reserved word in standard SQL ); INSERT INTO tbl VALUES ('A', 'Active', 1), ('A', 'Inactive', 2) , ('B', 'Active', 4), ('B', 'Inactive', 5) , ('C', 'Inactive', 7); -- ('C', 'Active') is missing Simple form - not fit for missing attributes
crosstab(text) with 1 input parameter:
SELECT * FROM crosstab( 'SELECT section, status, ct FROM tbl ORDER BY 1,2' -- needs to be "ORDER BY 1,2" here ) AS ct ("Section" text, "Active" int, "Inactive" int); Returns:
Section | Active | Inactive ---------+--------+---------- A | 1 | 2 B | 4 | 5 C | 7 | -- !!
- No need for casting and renaming.
- Note the incorrect result for
C: the value7is filled in for the first column. Sometimes, this behavior is desirable, but not for this use case. - The simple form is also limited to exactly three columns in the provided input query: row_name, category, value. There is no room for extra columns like in the 2-parameter alternative below.
Safe form
crosstab(text, text) with 2 input parameters:
SELECT * FROM crosstab( 'SELECT section, status, ct FROM tbl ORDER BY 1,2' -- could also just be "ORDER BY 1" here , $$VALUES ('Active'::text), ('Inactive')$$ ) AS ct ("Section" text, "Active" int, "Inactive" int);Returns:
Section | Active | Inactive ---------+--------+---------- A | 1 | 2 B | 4 | 5 C | | 7 -- !!
Note the correct result for
C.The second parameter can be any query that returns one row per attribute matching the order of the column definition at the end. Often you will want to query distinct attributes from the underlying table like this:
'SELECT DISTINCT attribute FROM tbl ORDER BY 1'
That's in the manual.
Since you have to spell out all columns in a column definition list anyway (except for pre-defined crosstabN() variants), it is typically more efficient to provide a short list in a VALUES expression like demonstrated:
$$VALUES ('Active'::text), ('Inactive')$$) Or (not in the manual):
$$SELECT unnest('{Active,Inactive}'::text[])$$ -- short syntax for long lists I used dollar quoting to make quoting easier.
You can even output columns with different data types with
crosstab(text, text)- as long as the text representation of the value column is valid input for the target type. This way you might have attributes of different kind and outputtext,date,numericetc. for respective attributes. There is a code example at the end of the chaptercrosstab(text, text)in the manual.
db<>fiddle here
Effect of excess input rows
Excess input rows are handled differently - duplicate rows for the same ("row_name", "category") combination - (section, status) in the above example.
The 1-parameter form fills in available value columns from left to right. Excess values are discarded.
Earlier input rows win.
The 2-parameter form assigns each input value to its dedicated column, overwriting any previous assignment.
Later input rows win.
Typically, you don't have duplicates to begin with. But if you do, carefully adjust the sort order to your requirements - and document what's happening.
Or get fast arbitrary results if you don't care. Just be aware of the effect.
Advanced examples
Pivot on Multiple Columns using Tablefunc - also demonstrating mentioned "extra columns"
\crosstabview in psql
Postgres 9.6 added this meta-command to its default interactive terminal psql. You can run the query you would use as first crosstab() parameter and feed it to \crosstabview (immediately or in the next step). Like:
db=> SELECT section, status, ct FROM tbl \crosstabview Similar result as above, but it's a representation feature on the client side exclusively. Input rows are treated slightly differently, hence ORDER BY is not required. Details for \crosstabview in the manual. There are more code examples at the bottom of that page.
Related answer on dba.SE by Daniel Vérité (the author of the psql feature):
8SELECT section, SUM(CASE status WHEN 'Active' THEN count ELSE 0 END) AS active, --here you pivot each status value as a separate column explicitly SUM(CASE status WHEN 'Inactive' THEN count ELSE 0 END) AS inactive --here you pivot each status value as a separate column explicitly FROM t GROUP BY section You can use the crosstab() function of the additional module tablefunc - which you have to install once per database. Since PostgreSQL 9.1 you can use CREATE EXTENSION for that:
CREATE EXTENSION tablefunc; In your case, I believe it would look something like this:
CREATE TABLE t (Section CHAR(1), Status VARCHAR(10), Count integer); INSERT INTO t VALUES ('A', 'Active', 1); INSERT INTO t VALUES ('A', 'Inactive', 2); INSERT INTO t VALUES ('B', 'Active', 4); INSERT INTO t VALUES ('B', 'Inactive', 5); SELECT row_name AS Section, category_1::integer AS Active, category_2::integer AS Inactive FROM crosstab('select section::text, status, count::text from t',2) AS ct (row_name text, category_1 text, category_2 text); Solution with JSON aggregation:
CREATE TEMP TABLE t ( section text , status text , ct integer -- don't use "count" as column name. ); INSERT INTO t VALUES ('A', 'Active', 1), ('A', 'Inactive', 2) , ('B', 'Active', 4), ('B', 'Inactive', 5) , ('C', 'Inactive', 7); SELECT section, (obj ->> 'Active')::int AS active, (obj ->> 'Inactive')::int AS inactive FROM (SELECT section, json_object_agg(status,ct) AS obj FROM t GROUP BY section )X Sorry this isn't complete because I can't test it here, but it may get you off in the right direction. I'm translating from something I use that makes a similar query:
select mt.section, mt1.count as Active, mt2.count as Inactive from mytable mt left join (select section, count from mytable where status='Active')mt1 on mt.section = mt1.section left join (select section, count from mytable where status='Inactive')mt2 on mt.section = mt2.section group by mt.section, mt1.count, mt2.count order by mt.section asc; The code I'm working from is:
select m.typeID, m1.highBid, m2.lowAsk, m1.highBid - m2.lowAsk as diff, 100*(m1.highBid - m2.lowAsk)/m2.lowAsk as diffPercent from mktTrades m left join (select typeID,MAX(price) as highBid from mktTrades where bid=1 group by typeID)m1 on m.typeID = m1.typeID left join (select typeID,MIN(price) as lowAsk from mktTrades where bid=0 group by typeID)m2 on m1.typeID = m2.typeID group by m.typeID, m1.highBid, m2.lowAsk order by diffPercent desc; which will return a typeID, the highest price bid and the lowest price asked and the difference between the two (a positive difference would mean something could be bought for less than it can be sold).
2Crosstab function is available under the tablefunc extension. You'll have to create this extension one time for the database.
CREATE EXTENSION tablefunc;
You can use the below code to create pivot table using cross tab:
create table test_Crosstab( section text, <br/>status text, <br/>count numeric) <br/>insert into test_Crosstab values ( 'A','Active',1) <br/>,( 'A','Inactive',2) <br/>,( 'B','Active',4) <br/>,( 'B','Inactive',5) select * from crosstab( <br/>'select section <br/>,status <br/>,count <br/>from test_crosstab' <br/>)as ctab ("Section" text,"Active" numeric,"Inactive" numeric) 
