how to shorten or optimize JOIN query in postgres - postgresql

Question

I got following query, in which I am joining 4 times. But it takes lot of time to return the result.
Is there any way to optimize this query ?
SELECT T1.wbd_date as WBD_DATE, to_char(T1.wbd_block_no, 'fm00') as BLOCK_NO, T2.wbd_value as AmbHum, T3.wbd_value as AmbTemp,
T4.wbd_value as SWT, T5.wbd_value as Expval
FROM (
SELECT wbd_attribute_id, wbd_date, wbd_block_no, wbd_value
FROM wb_block_data ) T1
JOIN wb_block_data T2 on T1.wbd_date = T2.wbd_date AND T1.wbd_block_no = T2.wbd_block_no and T2.wbd_attribute_id = 152112 and to_char(T2.wbd_date,'MM YYYY')='07 2019'
JOIN wb_block_data T3 on T1.wbd_date = T3.wbd_date AND T1.wbd_block_no = T3.wbd_block_no and T3.wbd_attribute_id = 152116 and to_char(T3.wbd_date,'MM YYYY')='07 2019'
JOIN wb_block_data T4 on T1.wbd_date = T4.wbd_date AND T1.wbd_block_no = T4.wbd_block_no and T4.wbd_attribute_id = 152120 and to_char(T4.wbd_date,'MM YYYY')='07 2019'
JOIN wb_block_data T5 on T1.wbd_date = T5.wbd_date AND T1.wbd_block_no = T5.wbd_block_no and T5.wbd_attribute_id = 150661 and to_char(T5.wbd_date,'MM YYYY')='07 2019'

Answer 1

You are essentially doing a pivot, doing that using conditional aggregation might be faster:
select wbd_attribute_id, block_no, wbd_date,
max(wbd_value) filter (where wbd_attribute_id = 152112) as AmbHum,
max(wbd_value) filter (where wbd_attribute_id = 152116) as AmbTemp,
max(wbd_value) filter (where wbd_attribute_id = 152120) as swt,
max(wbd_value) filter (where wbd_attribute_id = 152120) as Expval
from (
SELECT wbd_attribute_id, wbd_date, to_char(wbd_block_no, 'fm00') as block_no, wbd_value
FROM wb_block_data
where wbd_attribute_id in (152112, 152116, 152120, 150661)
and wbd_date >= DATE '2019-07-01'
and wbd_date < DATE '2019-08-01'
) t
group by wbd_attribute_id, wbd_date, block_no
You want an index on (wbd_attribute_id, wbd_date) for that.

Answer 2

An index such as the following might work:
CREATE INDEX idx ON wb_block_data (wbd_date, wbd_block_no, wbd_attribute_id);
However, we would also need to make the join conditions sargable:
SELECT T1.wbd_date as WBD_DATE, to_char(T1.wbd_block_no, 'fm00') as BLOCK_NO, T2.wbd_value as AmbHum, T3.wbd_value as AmbTemp, T4.wbd_value as SWT, T5.wbd_value as Expval
FROM
(
SELECT wbd_attribute_id, wbd_date, wbd_block_no, wbd_value
FROM wb_block_data
) T1
JOIN wb_block_data T2 on T1.wbd_date = T2.wbd_date AND T1.wbd_block_no = T2.wbd_block_no and T2.wbd_attribute_id = 152112 and T2.wbd_date >= '2019-07-01' and T2.wbd_date < '2019-08-01'
JOIN wb_block_data T3 on T1.wbd_date = T3.wbd_date AND T1.wbd_block_no = T3.wbd_block_no and T3.wbd_attribute_id = 152116 and T3.wbd_date >= '2019-07-01' and T3.wbd_date < '2019-08-01'
JOIN wb_block_data T4 on T1.wbd_date = T4.wbd_date AND T1.wbd_block_no = T4.wbd_block_no and T4.wbd_attribute_id = 152120 and T4.wbd_date >= '2019-07-01' and T4.wbd_date < '2019-08-01'
JOIN wb_block_data T5 on T1.wbd_date = T5.wbd_date AND T1.wbd_block_no = T5.wbd_block_no and T5.wbd_attribute_id = 150661 and T5.wbd_date >= '2019-07-01' and T5.wbd_date < '2019-08-01';
The only change I made to your query was to express the date requirement as a range, without using to_char:
wbd_date >= '2019-07-01' and wbd_date < '2019-08-01'
This is sargable, meaning that Postgres might able to use an index on the wbd_date column to satisfy the July, 2019 date range.

Answer 3

I changed query to this and with this I am getting desired result quickly
SELECT T1.wbd_date as WBD_DATE, to_char(T1.wbd_block_no, 'fm00') as BLOCK_NO, T2.wbd_value as AmbHum, T3.wbd_value as AmbTemp,
T4.wbd_value as SWT, T5.wbd_value as Expval
FROM (
SELECT wbd_attribute_id, wbd_date, wbd_block_no, wbd_value
FROM wb_block_data where to_char(wbd_date,'MM YYYY')='07 2019') T1
JOIN wb_block_data T2 on T1.wbd_date = T2.wbd_date AND T1.wbd_block_no = T2.wbd_block_no and T2.wbd_attribute_id = 152112
JOIN wb_block_data T3 on T1.wbd_date = T3.wbd_date AND T1.wbd_block_no = T3.wbd_block_no and T3.wbd_attribute_id = 152116
JOIN wb_block_data T4 on T1.wbd_date = T4.wbd_date AND T1.wbd_block_no = T4.wbd_block_no and T4.wbd_attribute_id = 152120
JOIN wb_block_data T5 on T1.wbd_date = T5.wbd_date AND T1.wbd_block_no = T5.wbd_block_no and T5.wbd_attribute_id = 150661