Postgresql – Error text: “Key … is not present in table” even though the key is there

constraintforeign keypostgresql

Using Postgresql 9.5 on Ubuntu 16.04. Importing large .csv files into a new database using COPY FROM. The database is created by the same script that attempts to import the .csv files, so I know the tables are initially empty. The script successfully imports around 45,000 rows into the first table.

The problem:
Partway through importing the 2nd table's data, I get errors like this one:

ERROR:  insert or update on table "inactive" violates foreign key constraint "inactive_drug_code_fkey"
DETAIL:  Key (drug_code)=(47543) is not present in table "qrym_drug_product".

But when I check the 1st table, I see that that key exists:

select * from dpd.qrym_drug_product where drug_code=47543;
  id   | drug_code | product_categorization | class | ...
-------+-----------+------------------------+-------+----
 17970 |     47543 |                        | Human | ...
(1 row)

Why would PostgreSQL complain about that key not being present in the table, when I can see it does exist?

I'm not using table inheritance (I saw the caveat on [1]).

Here is the first table:

\d dpd.qrym_drug_product;
                                       Table "dpd.qrym_drug_product"
           Column           |  Type   |                             Modifiers                              
----------------------------+---------+--------------------------------------------------------------------
 id                         | bigint  | not null default nextval('dpd.qrym_drug_product_id_seq'::regclass)
 drug_code                  | integer | not null
 product_categorization     | text    | 
 class                      | text    | 
 drug_identification_number | text    | 
 ai_group_no                | text    | 
Indexes:
    "qrym_drug_product_pkey" PRIMARY KEY, btree (id)
    "qrym_drug_product_drug_code_key" UNIQUE CONSTRAINT, btree (drug_code)
Referenced by:
    TABLE "dpd.inactive" CONSTRAINT "inactive_drug_code_fkey" FOREIGN KEY (drug_code) REFERENCES dpd.qrym_drug_product(id) ON DELETE RESTRICT

Here is the definition for the 2nd table that bombs partway through the COPY FROM:

\d dpd.inactive;
                                       Table "dpd.inactive"
           Column           |  Type   |                         Modifiers                         
----------------------------+---------+-----------------------------------------------------------
 id                         | bigint  | not null default nextval('dpd.inactive_id_seq'::regclass)
 drug_code                  | integer | not null
 drug_identification_number | text    | 
 brand_name                 | text    | 
 history_date               | date    | 
Indexes:
    "inactive_pkey" PRIMARY KEY, btree (id)
Foreign-key constraints:
    "inactive_drug_code_fkey" FOREIGN KEY (drug_code) REFERENCES dpd.qrym_drug_product(id) ON DELETE RESTRICT

Best Answer

Someone named "RhodiumToad" in the #postgresql channel on IRC pointed out the problem. Because I didn't explicitly state the column name, the 2nd table is referencing the primary key column "id" from the first table. Instead, I wanted it to reference the drug_code column.

So where I had previously defined the 2nd table as:

CREATE TABLE dpd.inactive
(
    id          BIGSERIAL NOT NULL UNIQUE PRIMARY KEY,
    drug_code   INTEGER NOT NULL REFERENCES dpd.qrym_drug_product,
    ...

I had to fix it up to be this:

CREATE TABLE dpd.inactive
(
    id          BIGSERIAL NOT NULL UNIQUE PRIMARY KEY,
    drug_code   INTEGER NOT NULL REFERENCES dpd.qrym_drug_product (drug_code),
    ...

Related Solutions

Postgresql – Postgres multiple joins slow query, how to store default child record

You write:

Each customer can have multiple sites, but only one should be displayed in this list.

Yet, your query retrieves all rows. That would be a point to optimize. But you also do not define which site is to be picked.

Either way, it does not matter much here. Your EXPLAIN shows only 5026 rows for the site scan (5018 for the customer scan). So hardly any customer actually has more than one site. Did you ANALYZE your tables before running EXPLAIN?

From the numbers I see in your EXPLAIN, indexes will give you nothing for this query. Sequential table scans will be the fastest possible way. Half a second is rather slow for 5000 rows, though. Maybe your database needs some general performance tuning?

Maybe the query itself is faster, but "half a second" includes network transfer? EXPLAIN ANALYZE would tell us more.

If this query is your bottleneck, I would suggest you implement a materialized view.

After you provided more information I find that my diagnosis pretty much holds.

The query itself needs 27 ms. Not much of a problem there. "Half a second" was the kind of misunderstanding I had suspected. The slow part is the network transfer (plus ssh encoding / decoding, possibly rendering). You should only retrieve 100 rows, that would solve most of it, even if it means to execute the whole query every time.

If you go the route with a materialized view like I proposed you could add a serial number without gaps to the table plus index on it - by adding a column row_number() OVER (<your sort citeria here>) AS mv_id.

Then you can query:

SELECT *
FROM   materialized_view
WHERE  mv_id >= 2700
AND    mv_id <  2800;

This will perform very fast. LIMIT / OFFSET cannot compete, that needs to compute the whole table before it can sort and pick 100 rows.

pgAdmin timing

When you execute a query from the query tool, the message pane shows something like:

Total query runtime: 62 ms.

And the status line shows the same time. I quote pgAdmin help about that:

The status line will show how long the last query took to complete. If a dataset was returned, not only the elapsed time for server execution is displayed, but also the time to retrieve the data from the server to the Data Output page.

If you want to see the time on the server you need to use SQL EXPLAIN ANALYZE or the built in Shift + F7keyboard shortcut or Query -> Explain analyze. Then, at the bottom of the explain output you get something like this:

Total runtime: 0.269 ms

Sql-server – SQL Server 2005, Foreign key check against part of a table

No this isn't possible.

I'd probably create a separate table categoriesWithArticles that holds the relevant categoryids (instead of having the flag) and have the FK reference that table instead.

Another more convoluted way to enforce it and keep the column would be

CREATE TABLE categories
(
categoryId int primary key,
hasarticles bit not null,
unique(categoryId, hasarticles)
)

CREATE TABLE articles
(
categoryId int,
hasarticles as cast (1 as bit) persisted,
FOREIGN KEY (categoryId, hasarticles) REFERENCES categories(categoryId, hasarticles)
)

But this requires the creation of a technically redundant unique constraint as well as the additional persisted column in the articles table.

Best Answer

Related Solutions

Postgresql – Postgres multiple joins slow query, how to store default child record

pgAdmin timing

Sql-server – SQL Server 2005, Foreign key check against part of a table

Related Question