![]() This is a difficult problem because getting that info from another transaction would violate the I in ACID. ![]() ![]() The error can be suppressed with ON CONFLICT DO NOTHING, but the query will return an empty set instead of the new row. If the entry does not already exist, the INSERT will fail with a unique constraint violation. NOTE: There is a race condition present here and in the original answer. The LIMIT 1 at the end allows the planner to short-circuit further processing/iteration once it knows there's an answer available. The UNION ALL tells the planner it doesn't have to collect results for de-duplication. the query engine to cut processing short for the INSERT ) LIMIT 1 - Just return whatever comes first in the results and allow If we reach this point in iteration, we needed to do the INSERT and Don't check for duplicates to be removed marginally faster for the much more common read-only case. Marginally slower for the insert case, but also This comes first in the UNION ALL since it'll almost certainly be Only insert when we don't find anything, avoiding a table lock if Minor tweak a decade late to Denis's excellent answer: - Create the table with a unique constraint In my query you "check if a value not exists" only on id that is a integer primary key, that, for construction, is fast. This query needs to search for the value other_key only once, and is a "search this value" not a "check if this value not exists in the table", that is very heavy in Denis alternative you use other_key in both types of searches. That if id is already in mytable I don't insert anything.Īt the end I put everything together with a UNION between table_ins and table_sel, so that I'm sure to take my sweet id value and execute both CTE. COALESCE(id, NEXTVAL('mytable_id_seq'::REGCLASS)) is saying: id could be defined, if so, use it whereas if id is null, increment the sequence on id and use this new value to insert a row. In table_ins CTE I try to insert the same row I was looking for earlier. If I don't find it, I assure that table_sel returns at least one row, with a union with a SELECT NULL. To do so, run the \dt command: \dt Let’s say we need to insert data into the teaminfo table. In table_sel CTE I'm looking for the right row. Step 1: Select a Table Using \dt Command Firstly, select a table where you want to insert the data. ![]() I have an alternative to Denis answer, that I think is less database-intensive, although a bit more complex: create table mytable (id serial primary key, other_key varchar not null unique) ĬOALESCE(id, NEXTVAL('mytable_id_seq'::REGCLASS)), ![]()
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