Postgresql – Need help with correlated subquery

postgresqlsubqueryupdate

I have two PostgreSQL tables that each contain a column called date_of_incident.

They each also have a column called incident_id and this is how the tables are related.

I want to update all rows of table 1 by setting date_of_incident equal to date_of_incident from the corresponding row of table 2 where incident_id from table 1 equals incident_id from table 2.

Can anyone can give a sample UPDATE? I'd appreciate it.

incident_id is unique in both tables and it is how the tables are related, though not by foreign key or constraint (sadly). I have the extra condition of status = closed. The only complication is that table 1 has a trigger function on update and I need to examine to see how the SQL will affect things.

Best Answer

Postgres allows to join tables in an UPDATE statement:

update table_1
   set date_of_incident = t2.date_of_incident
from table_2 t2
where table_1.incident_id = t2.incident_id;

This assumes that incident_id is unique in both tables.

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Sql-server – Querying multiple tables

This will get you the Status Description:

SELECT s.SR_Service_RecID, SR_Status.Description, c.Company_Name, s.Last_Update, s.Date_Req
FROM SR_Service s 
    INNER JOIN Company c ON s.Company_RecID = c.Company_RecID
    INNER JOIN SR_Status ON s.ST_Status_RecID = SR_Status.SR_Status_RecID
WHERE SR_Type_RecID IN (SELECT t.SR_Type_RecID
                        FROM SR_Type t 
                        INNER JOIN SR_Board b
                            ON t.SR_Board_RecID = b.SR_Board_RecID
                        WHERE t.description LIKE @Type
                           AND b.Board_Name LIKE @Board)
AND s.SR_Status_RecID IN (SELECT SR_Status_RecID
                          FROM SR_Status
                          WHERE Closed_Flag = 0)

To add the schedule, you'd need to add a key field from the schedule table to the SR_Service table.

Sql-server – Help with tricky update statement

The performance impact from multiple logical reads could be a result of your UDF.

Provided is a great article which describes using inline table-valued UDFs to reduce the row-by-row calls to the scalar UDF. UPDATE: I noticed you were already using table-valued UDF.

http://dataeducation.com/scalar-functions-inlining-and-performance-an-entertaining-title-for-a-boring-post/

To replicate your scenario, I executed the following query:

DECLARE
   @Measurements TABLE(Precidence int, -- the relative scale of a measurement
             Measurement varchar(max), -- Grams, Kilograms, Liters, etc
             MeasurementType varchar(max)); -- Weight, Volume, etc`

DECLARE
   @Items TABLE(ItemType varchar(max),   
            Quantity float,  
            Measurement varchar(max),   
            ToMeasurement varchar(max));

insert into @items (ItemType, Quantity, Measurement) values ('Widget','1','G');  
insert into @items (ItemType, Quantity, Measurement) values ('Widget','1','KG');  
insert into @items (ItemType, Quantity, Measurement) values ('Widget','1','ML');  
insert into @items (ItemType, Quantity, Measurement) values ('Widget','1','L'); 

insert into @Measurements (Precidence, Measurement, MeasurementType) values ('2','G','Weight');  
insert into @Measurements (Precidence, Measurement, MeasurementType) values ('1','KG','Weight');  
insert into @Measurements (Precidence, Measurement, MeasurementType) values ('1','GAL','Volume');  
insert into @Measurements (Precidence, Measurement, MeasurementType) values ('2','L','Volume');  
insert into @Measurements (Precidence, Measurement, MeasurementType) values ('3','ML','Volume');

Afterwards, I complied and executed the following update statement:

WITH Items_CTE AS
   (
        SELECT A.ItemType, 
               A.Quantity,
               A.Measurement,  
               (SELECT TOP 1 M.Measurement FROM @Measurements M
                JOIN @Items C ON C.Measurement = M.Measurement
                WHERE M.MeasurementType = B.MeasurementType
                AND  C.ItemType = A.ItemType
                 ORDER BY Precidence)ToMeasurement
       FROM @Items A
       JOIN @Measurements B
       ON A.Measurement = B.Measurement
    )  
UPDATE @Items  
SET ToMeasurement = cte.ToMeasurement  
FROM ITEMS_CTE as cte
JOIN @Items as i
ON cte.measurement = i.measurement;

The UPDATE statement uses a CTE and the results were as follows:

ItemType | Quantity | Measurement | ToMeasurement  
Widget   |    1     |    G        |    KG  
Widget   |    1     |    KG       |    KG  
Widget   |    1     |    ML       |    L  
Widget   |    1     |    L        |    L

Best Answer

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Sql-server – Querying multiple tables

Sql-server – Help with tricky update statement

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