Update with left join postgres

Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Asked 7 years, 9 months ago. Active 7 years, 9 months ago. Viewed 9k times. Update T1 Set T1. Amount - T2. Improve this question. Akhilesh Akhilesh 1 1 gold badge 12 12 silver badges 40 40 bronze badges. Add a comment. Active Oldest Votes. Improve this answer. Postgresql update joins subquery basically means to update the join statement.

We have taken the examples of the tables which we created earlier i. Self-join in PostgreSQL is generally a query to merge the same tables with different aliases. For performing a self-join, we have to reference the same table two times but with various aliases to discard confusion between tables. The self-join is checked as a joining of two copies of the same table.

We have to set the comparison and eliminate the condition of the same rows. The syntax for self-join is the same as normal joins. The only difference is that this time the Table2 table will also be the same as Table1. Basically, we have to update the self-join statement.

Read: Postgresql Sum — How to use. Read: Postgresql while loop. Firstly, we will choose those columns that we want to group e. If we are trying to update the table1 with the corresponding row from table2 , we want to use the WHERE clause. We have a table named weather and here is the update query for it. Query performance in Postgresql is generally affected by many things. Some of these can be manipulated by the user, while others are basic to the underlying design of the system.

This topic provides some suggestions about understanding and controlling PostgreSQL performance. PostgreSQL comes up with a query plan for every query it is given. We determine the right plan to match the query structure and the properties of the data is definitely critical for better performance. Rows output is quite difficult since it is not the number of rows processed or scanned by the query which is usually less, reflecting the estimated selectivity of any WHERE -clause conditions that are being applied at this code.

Generally, the top-level row counts an approximate number of rows really returned, updated, or deleted by the query. I guess the performance would be the same. The second one should work at first sight what is the error you get?.

The second one will update all the records in Users table, not just the "Users u". Add a comment. Active Oldest Votes. Improve this answer. Thanks for answering. It seems that what I'm asking cannot be done.

I mean in case of query 2 there is not a way to reference u table somehow. Anyway I'll have in mind your solution for future reference and possible more complex queries. For now I'll go with the 3rd query. Clive Paterson Clive Paterson 1, 1 1 gold badge 14 14 silver badges 10 10 bronze badges.

I don't have Postgres installed anymore and it's been 2 years since I last used it, but I believe your query is not syntactical correct. Otherwise my first query would work as well. If I remember correct, in Postgres you can't alias the table you are updating.

You cannot use that alias in the SET clause. Sign up or log in Sign up using Google. Sign up using Facebook.