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Graph/sql-dedup-filter-inefficiency

Pattern

SQL Rewrite Missing Semantics

sql-dedup-filter-inefficiency

SQL attempts to filter or deduplicate rows by subquery membership and window ranking often get rewritten into inefficient UNIONs or joins; without correct join predicates and EXISTS/window logic, queries silently return wrong sets or time out.

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Updated6/28/2026

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one failed write aborted the rest of the batch — structured post-turn extraction wrote events and beliefs without per-entry error isolation. Outcome: leaving future event inserts vulnerable once the initial partition window expired.

I can get the same performance issues with either a select or a delete — they join two tables, and none of the join conditions compares using `=`. Tension: `IS NOT DISTINCT FROM` is not supported by indexes, and `OR` is usually a performance problem anyway. Outcome: the root of your problem are the NULL values.

When any source table had zero rows, that table was silently absent from the result — A dashboard query unioned several content tables into a CTE then GROUP BY'd the table_name to emit one summary row per table. Tension: one summary row per table.

got extra junk rows — SQLAlchemy filter on Query again. Outcome: simplify that down using joins and avoids having subqueries.

datetime arithmetic using intervals is not directly supported on MySQL

error: could not determine data type of parameter [REDACTED] — Extended a Postgres SQL query in TypeScript (pg driver) to support optional filters. Outcome: Result: `error: could not determine data type of parameter [REDACTED]` on query execution.

none of the three queries you showed ended up using it — Select * from users where Type = 'SomeType' and First = 'SomeName1' Order by CreatedAt DESC;. Tension: The fact that you're selecting and ordering by `CreatedAt` doesn't mean it's needed as an index key. Outcome: If you simply remove `createdat` from the index, they're happy to use it for a Bitmap Index Scan taking below `5ms`.

ERROR: duplicate key value violates unique constraint "orders_pkey" — using a LEFT JOIN with WHERE o.order_id IS NULL. Tension: This query should only insert `order_id`s that do not already exist in `orders`. Outcome: Use ON CONFLICT DO NOTHING.

in which the query above is nested. Tension: why is it a must to alias in the second query and not the first ?

Now I want to keep only the rows where we have multiple times the same ID and Name combination. — using the row_number() functon to identify duplicates, partitioned by ID and Name. Tension: the third, fourth and last row should be removed. Outcome: How can this be done?

The following is the method I use. It is very bloated and the execution time is too long. — especially if there are more score columns(score8, score9...), more `UNION ALL` will be piled up.

I get no results — if I turn around and select from this table using this value such as. Tension: The table column seems to have a 6 millisecond precision that the select statement does not reflect. Outcome: It seems like no matter what I do I'm stuck with a precision of 3 millisecond decimal places when selecting.

"too many range table entries" error — I'm trying to update a partitioned PostgreSQL table using a PL/pgsql loop. Tension: it contains a self join on a large table. Outcome: If I hardcode the partition to update in the WHERE clauses, it works just fine.

SQL functions cannot return type trigger. Tension: functions written in standard SQL can't return triggers. Outcome: That's not possible.

Outcome: I also tried a few variations of the same query (got same error).

The recordset produced by the SQL query was empty when executed as a single script (dropping/creating temp tables and then selecting from them).

Filter rows from a table so that records with sensorfield1 flag = 'r' are selected, except for IDs that have corresponding rows with flag = 'h'; for IDs where flag value is only 'h', include those rows as well. Denodo throws an error when attempting a solution using analytic/window functions: '(function) is not executable'.

I see the expected results using above query. — Now I want to remove the entries from above result which are in table2. Tension: Is there a more efficient of achieving the same result? and are there any cases that I could be missing?

An INSERT...SELECT cron job is too slow because it aggregates 200K groups from data_time_series and conditionally inserts rows into storage_time_series using a NOT EXISTS subquery. The conditional existence check becomes a performance bottleneck.

How to translate an Excel named range (a collection of variant cell values) into a SQL representation so that functions like SUM can operate naturally over the range, ideally skipping values that don't make sense.

Implementing cursor-based pagination in Knex/Postgres using a tuple comparison like `(timestamp, id) > (cursor.timestamp, cursor.id)` fails and returns no rows. The attempted Knex query with two separate `where` clauses behaves like an `AND` comparison rather than the intended tuple `>` semantics.

more than one row returned by a subquery used as an expression.

When sensitive fields are encrypted in PostgreSQL, queries using WHERE (e.g., exact match) cannot efficiently filter rows because the encrypted values cannot be compared without decrypting them. This makes encrypted-field searches slow and impractical at scale.

Sigma rules do not work reliably on Sysmon .csv logs

String predicate handling still allows arbitrary SQL and information disclosure

Executing the same SQL query from application code annotated with @Transactional causes much heavier locking behavior than running the raw SQL directly in SQL Server. The lock types and scope (key range vs scans/parallelism) differ between the two execution paths.

its giving me error saying you have syntax error in your SQL — in a JDBC program, writing the following code. Tension: When I am doing this using MySQL command line client, its wrking perfectly. But if I try to do this in a JDBC program. Outcome: I found a little issue in your code.

Trying to replace a working native Postgres query that uses ARRAY_AGG with a non-native Spring Data JPA query and projection. Hibernate throws a SemanticException related to using ordered set aggregate functions (array_agg) without the required WITHIN GROUP/OVER clause.

Duplicate schema files and missing vendor role in SQLite ecommerce project. — Found two conflicting schema.sql files with different table structures and roles. Tension: Needed to consolidate into a single schema with WAL mode, indexes, and vendor role.

Duplicate detection in an agent-driven Q&A system adds significant synchronous write-path latency when it embeds and cosine-compares before inserting. Additionally, downstream knowledge-graph entity extraction can create duplicate nodes due to concurrent merges without proper uniqueness enforcement.

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