How to rewrite some values in query? - PostgreSQL

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I have got a query which result is in table1

-------------------------
|column1|column2|column3|
-------------------------
|   v1  |   30  |  40   |
|   v1  |   34  |  41   |
|   v1  |   35  |  42   |
|   v2  |   30  |  40   |
|   v2  |   34  |  41   |
|   v2  |   35  |  42   |
-------------------------

I want to change duplicated values to NULL in first column, (i.e).

-------------------------
|column1|column2|column3|
-------------------------
|   v1  |   30  |  40   |
| null  |   34  |  41   |
| null  |   35  |  42   |
|   v2  |   30  |  40   |
| null  |   34  |  41   |
| null  |   35  |  42   |
-------------------------

What should I do with table1?

You can use row_number() function:

select (case when row_number() over (partition by col1 order by col1) > 1 
             then null else col1 end) col1, 
        col2, col3
from table t;

However, you can also use lag() function

select (case when lag(col1) over (partition by col1 order by col1) = col1 
                  then null else col1 end) col1, 
        col2, col3
from table t;

Documentation: 9.5: VALUES Lists, VALUES provides a way to generate a "constant table" that can be used in a query without having to actually create and populate a table on-disk. it differently, so it's usually better to override the default names with a table alias list​, like this: In PostgreSQL, these can be implemented using functions and triggers as well. The rule system (more precisely speaking, the query rewrite rule system) is totally different from stored procedures and triggers. It modifies queries to take rules into consideration, and then passes the modified query to the query planner for planning and execution.

try this:

SELECT CASE WHEN D.RN = 1 THEN column1 ELSE NULL END AS column1
    ,column2
    ,column3
FROM(
    SELECT *
        , ROW_NUMBER() OVER(PARTITION BY column1 ORDER BY column1)RN
    FROM Your_table
    )D

PostgreSQL UPDATE, If you update values in multiple columns, you use a comma (,) to separate To verify the update, you can select data from the link table as the following query:. > Are there any plans for implementing query rewriting (i.e. allowing the > optimizer to substitute materialized views for queries) > in upcoming versions? I have recently seen this answer, saying that query > rewriting could be achieved using the rules system, but > I could not figure out how to. Could someone please give me some tips on how

You can try this query.

using ROW_NUMBER function to make rowNumber,then CASE When Expression to show the first column1 else be null

ORDER BY (SELECT 1) can let your data be the original order.

select CASE WHEN rn = 1 THEN  column1 ELSE NULL END,
       column2,
       column3
from 
(
  SELECT column1,
         column2,
         column3,
         ROW_NUMBER() OVER(PARTITION BY column1 ORDER BY (SELECT 1)) rn 
  FROM T
) t

sqlfiddle:http://sqlfiddle.com/#!15/fcf3d/1

Modifying Rows with UPDATE - Practical PostgreSQL [Book], It instructs PostgreSQL to update the value in the stock table's retail column with the booktown=# SELECT retail FROM stock booktown-# WHERE isbn The expression itself has several components, separated by parentheses to enforce  In addition, PostgreSQL executes the query with the IN operator much faster than the same query that uses a list of OR operators. PostgreSQL NOT IN operator. You can combine the IN operator with the NOT operator to select rows whose values do not match the values in the list. The following statement find all rentals with the customer id is not 1 or 2.

SELECT CASE WHEN RN=1 THEN
          "column1"
       ELSE
          NULL
       END AS "column1",
       "column2", "column3"
FROM
(
SELECT 
"column1", "column2", "column3",
ROW_NUMBER() OVER  (PARTITION BY "column1" ORDER BY "column1") AS RN
FROM Table1
) AS T

Ouput

column1 column2 column3
v1      30      40
(null)  34      41
(null)  35      42
v2      30      40
(null)  34      41
(null)  35      42

Demo

http://sqlfiddle.com/#!17/5b2e1/9

PostgreSQL: How to update large tables, When you update a value in a column, Postgres writes a whole new row in the disk some data types does not require a full table rewrite since Postgres 9.2. If you are running the queries in a live database you may need to  The PostgreSQL SUM function returns the sum of values or distinct values. The syntax of the SUM function is as follows: SUM(DISTINCT column) There are some important points you should remember when using the SUM function: The SUM function ignores NULL values. It means the NULL values are not considered in the calculation of the SUM function.

My Favorite PostgreSQL Queries and Why They Matter, Yet, for some reason, the second month did not pull its weight and we Let's rewrite this query and use ORDER BY NULLS first on the legit column. Now the IN predicate contains multiple rows of one column's values to  CREATE RULE defines a new rule applying to a specified table or view. CREATE OR REPLACE RULE will either create a new rule, or replace an existing rule of the same name for the same table. The PostgreSQL rule system allows one to define an alternative action to be performed on insertions, updates, or deletions in database tables.

Faster PostgreSQL Counting, In Postgres, there are ways to count orders of magnitude faster. Let's begin at the beginning, exact counts allowing duplication over some or all of a table, reltuples) VALUES ('items', (SELECT count(*) from items)); CREATE OR non-​zero and Citus will rewrite count distinct query plans to use HLL. The ANY operator returns true if any value of the subquery meets the condition, otherwise, it returns false. Note that SOME is a synonym for ANY, meaning that you can substitute SOME for ANY in any SQL statement. PostgreSQL ANY examples. We will use the following film and film_categorytables in the sample database for the demonstration.

PostgreSQL REPLACE() function, In the example below, the specified string 'st' have been replaced by '**' in the string 'test string'. Code: SELECT replace('test string', 'st', '**');. Rewrite: We can change or alter the client query programmatically. We are using python for routing and rewriting and PostgreSQL as a database. So we expect some basic understanding of these