Postgres 14

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Help with an interesting Postgres question: Why isn't an Index Only Scan used on a partition accessed via the parent table?.

CREATE TABLE tab(
    email     VARCHAR(20)
)

CREATE TABLE

INSERT INTO tab VALUES
('sam@gmail.com'),
('max@gmail.com'),
('guy.brush@gmail.com'),
('in.diana@gmail.com');

INSERT 0 4

SELECT REGEXP_REPLACE(email, '@.*', '@test.com')
FROM tab

regexp_replace

sam@test.com

max@test.com

guy.brush@test.com

in.diana@test.com

SELECT 4

UPDATE tab
SET email = REGEXP_REPLACE(email, '@.*', '@test.com');

UPDATE 4

SELECT * 
FROM tab

email

sam@test.com

max@test.com

guy.brush@test.com

in.diana@test.com

SELECT 4