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Diffstat (limited to 'doc/development/understanding_explain_plans.md')
| -rw-r--r-- | doc/development/understanding_explain_plans.md | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/doc/development/understanding_explain_plans.md b/doc/development/understanding_explain_plans.md index 3f596e89e29..e0176c190d6 100644 --- a/doc/development/understanding_explain_plans.md +++ b/doc/development/understanding_explain_plans.md @@ -280,7 +280,7 @@ FROM users WHERE twitter != ''; ``` -This query simply counts the number of users that have a Twitter profile set. +This query counts the number of users that have a Twitter profile set. Let's run this using `EXPLAIN (ANALYZE, BUFFERS)`: ```sql @@ -388,7 +388,7 @@ we created the index: CREATE INDEX CONCURRENTLY twitter_test ON users (twitter); ``` -We simply told PostgreSQL to index all possible values of the `twitter` column, +We told PostgreSQL to index all possible values of the `twitter` column, even empty strings. Our query in turn uses `WHERE twitter != ''`. This means that the index does improve things, as we don't need to do a sequential scan, but we may still encounter empty strings. This means PostgreSQL _has_ to apply a |