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Graph/50dd58b2-c11a-4fa6-a235-0070f730f16a

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50dd58b2-c11a-4fa6-a235-0070f730f16a

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Updated5/1/2026

PageRank0.0001

Effectiveness0.000

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9 linked nodes

PERTAIN_TORootCause

lastIndexOf(String, int) uses fromIndex as an inclusive upper bound and searches backward from that position, so passing the last match index can return the same match again

PERTAIN_TOProblem

String.lastIndexOf(str, index) returns the same match position unexpectedly when called with the previous match index

PERTAIN_TOSolution

Pass lastIndex - 1 to lastIndexOf() when looking for the previous occurrence

PERTAIN_TOProblem

how to filter orders with the remark field containing certain word? — my model order has a text field as: order.remark. Tension: user might type in a lot of information without enter space. Outcome: how to effectively filter the orders?

PERTAIN_TOSolution

You can use contains() method for string — filter orders with the remark field containing certain word. Outcome: You can use contains() method for string.

PERTAIN_TORootCause

the words are not seperated by space or tab or any sort of delimeters — user might type in a lot of information without enter space. Tension: how to filter orders with the remark field containing certain word?

PERTAIN_TOAnswer

The index isn't used because `LIKE '%@example.com'` has a **leading wildcard**. B-tree indexes only work for prefix matches (`LIKE 'foo%'`), not suffix/infix patterns. **Solutions, from simplest to most powerful:** 1. **Reverse index for suffix search:** ```sql CREATE INDEX idx_email_reverse ON users (reverse(email)); -- Query: SELECT * FROM users WHERE reverse(email) LIKE reverse('%@example.com'); -- Becomes: WHERE reverse(email) LIKE 'moc.elpmaxe@%' ← prefix match, uses index ``` 2. **Functional index on domain:** ```sql CREATE INDEX idx_email_domain ON users (split_part(email, '@', 2)); -- Query: SELECT * FROM users WHERE split_part(email, '@', 2) = 'example.com'; ``` This is the cleanest if you're always searching by domain. 3. **pg_trgm for general LIKE/ILIKE:** ```sql CREATE EXTENSION IF NOT EXISTS pg_trgm; CREATE INDEX idx_email_trgm ON users USING gin (email gin_trgm_ops); -- Now this uses the index: SELECT * FROM users WHERE email LIKE '%@example.com'; ``` `pg_trgm` GIN indexes support arbitrary substring matches including leading wildcards. This is the most flexible solution. 4. **Full-text search** — overkill for emails, but worth knowing for general text columns. For 2M rows, option 2 or 3 will bring your query from 10+ seconds to single-digit milliseconds.

PERTAIN_TOProblem

PostgreSQL query on a large users table is slow because `LIKE "%@example.com"` does not use the email index

PERTAIN_TOSolution

Use a reverse() functional index for suffix search, or create a pg_trgm GIN index for arbitrary substring matching

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